search: prevent username related conditions from removing "stop words"

Before this revision, username related conditions below cause
unintentional ignorance of "stop words".

- owner: (for all)
- author: (for "Commit messages")

Therefore, username related conditions with "this", "a", "you", and so
on are completely ignored, even if they are valid username components.

To prevent username related conditions from removing "stop words",
this revision explicitly specifies "analyzer" for username related
fields of SCHEMA and CHGSETS_SCHEMA.

Difference between EMAILADDRANALYZER and default analyzer of TEXT is
whether "stop words" are preserved or not. Tokenization is still
applied on usernames.

For future changing, this revision doesn't make EMAILADDRANALYZER
share analyzer definition with PATHANALYZER, even though their
definitions are identical with each other at this revision.

This revision requires full re-building index tables, because indexing
schemas are changed.

Original patch has been modified by Mads Kiilerich - tests of 'owner' will be
addressed separately.