scm: refactor install_git_hooks

Rename, simplify, and negate some logic to make the flow more readable to me
and give better logging.

For example, "force_create" were more about "force overwrite". Calling it
"force" is more precise.

py3: migrate from urllib2 to urllib

Based on 2to3 urllib, but with unnecessary imports removed.

py3: trivial renaming of .iteritems() to .items()

A bit like "2to3 -f dict", but we don't want list().

vcs: drop unused get_hook_location (Issue #353)

Also, the hg implementation was odd - the '.hgrc' directory name looks very
similar to 'hgrc' but could be anything, such as 'hooks'.

py3: add b'' annotations in some places where they will be needed later

Mostly entirely trivial adding of b prefix that is a ignored for py2 ... and
also a bit of related trivial reformatting/refactorings.

vcs: always return bytes from node.content

We will rather have the unicode conversions explicit.

Note: Py3 bytes doesn't have .startswith - replace that with a regexp.

vcs: change get_diff to use _run_git_command directly

This will allow run_git_command to return strings while get_diff still return
raw bytes.

vcs: drop unused _diff_name_status

It popped up as something to do for py3. Don't waste time on it.

py3: use explicit octal literals

From 2to3 numliterals.

cleanup: use isinstance instead of comparing types

From 2to3 idioms.

vcs: introduce 'branches' attribute on changesets, making it possible for Git to show multiple branches for a changeset

Mercurial changesets will always have have exactly one branch (which might be
"default"). The VCS data model was the same.

Git allows for a changeset to have 0 or more branches ... and possibly one of
them as active. The right data model is thus to have an enumerable of branches.

We thus add a 'branches' attribute and use it where applicable.

The existing 'branch' attribute used some heuristics to decide which branch use
as "the" branch ... and in some places code (and tests) rely on that. We thus
keep that old method, knowing that some of its uses probably should move to
'branches'.

The code for retrieving Git branches is based on work by Dominik Ruf.

vcs: sanitize diff context values (Issue #306)

- Updated Git repository implementation to ensure context falls within
0 to 2**31-1 range (inclusive) when fetching a diff.
- Added tests for Git repositories for checking passed-in negative and
overflowing contexts (for the --unified option).
- Updated Mercurial repository implementation to ensure context is not
negative when fetching a diff.
- Added tests for Mercurial repositories for checking passed-in
negative context (for the --unified option).

codingstyle: replace upper-case variable names with lower-case ones

PEP8 issues reported by flake8.

codingstyle: trivial whitespace fixes

Reported by flake8.

tests: put all temporary files in one top directory

Use KALLITHEA_TESTS_TMP_PATH or a create a temporary /tmp/kallithea-test-*
directory.

Some temporary files might still be placed in /tmp ... but nothing should be
left behind.

vcs: fix repo size calculation

tip.walk already 'dives into' the dirs - don't do that twice.

tests: fix Git on Windows sometimes failing on ' or ` in file:/// URLs

Some Git versions will fail when cloning a repository like:

git clone file:///path/to/strange-file-'`foobar myclone

Since '` (and some other characters) are filtered anyway (in
lib.utils.repo_name_slug) I think this test doesn't need to test those
characters.

vcs: better handling of invalid email addresses: don't consider them email addresses

13da89053853 was in principle right in always returning email adresses as
string ... but unfortunately the function also returned invalid email addresses
that didn't fit into strings.

To fix this, the function is refactored to always use regexp matching of valid
email addresses ... and to be simpler. The behaviour should be the same as
before for all valid email addresses.

remove vestiges of Python 2.5 support

We only support Python 2.6 and 2.7; hence we do not need to import
with-statement support from __future__.

git: run external commands as list of strings so we really get correct quoting (Issue #135)

a6dfd14d4b20 from
https://bitbucket.org/conservancy/kallithea/pull-request/17/add-quotes-to-repo-urls-for-git-backend
fixed that issue but did not make it "safe". The vcs git backend still used
command strings but tried to quote them correctly ... but that approach is
almost impossible to get right.

Instead, pass a string list all the way to the subprocess module and let it do
the quoting. This also makes some of the code more simple.

tests: avoid executing tests in base classes

Fixes lots of failures with pytest by making sure base test classes don't
inherit from unittest.TestCase or by prefacing name with an underscore so tests
don't get executed by pytest.

Escape shell command parts for Git backend

Python 2.x uses pipes.quote and Python 3.3+ uses shlex.quote in
GitRepository._run_git_command()

Second step in two-part process to rename directories.
This is the actual directory rename.