.hgignore: Add .eggs/ and tarballcache/

Setuptools >= 7.0 and .eggs is created and populated with eggs if setup.py has
setup_requires of packages that are not installed and setuptools has to
download them to satisfy the requirements. See
https://bitbucket.org/pypa/setuptools/pull-request/97/cache-eggs-required-for-building-in-eggs/diff#

tarballcache comes from test.ini : archive_cache_dir = %(here)s/tarballcache