* Now checking if a commit is already reverted or there is a conflict is
  much more faster.
* No longer need to create a new branch.

* Not required to run hooks since it's an internal commit

If path_with_namespace is nil Repository#raw_repository will also return
nil. Apparently code out there creates a Repository instance without a
namespace path. Right.

Just checking raw_repository is no longer accurate to determine if a
repository exists or not.

Now that Repository#raw_repository no longer sets the autocrlf option it
will also no longer raise any NoRepository errors since it doesn't
access Rugged any more. This also means that Repository#exists? can't
simply return the raw repository as this is no indication of whether or
not the repository actually exists (besides returning a non boolean is
weird in the first place).

To solve this problem Repository#exists? now properly checks if the
repository exists and returns true/false instead of a
Gitlab::Git::Repository or nil object.

Setting the "autocrlf" Git option is an overkill since it's rarely
actually needed. More importantly, it has quite the impact on
performance (see gitlab-org/gitlab-ce#13457 for more information).

By setting "autocrlf" when creating or updating files we guarantee the
option is always set properly when we actually need it _without_
introducing overhead for requests that have nothing to do with this
option.

Fixes gitlab-org/gitlab-ce#13457

This ensures that _all_ caches (including any caches normally only
flushed under certain conditions) are flushed whenever a project is
removed. Because cache keys are based on project namespaces (excluding
IDs) not doing so could result in a newly created project re-using old
caches (if the project was re-created using the same name).

This ensures the caches for Repository#empty? and
Repository#has_visible_content? are flushed after a repository has been
imported or forked.

Fixes gitlab-org/gitlab-ce#13505

The "default_branch" argument is never used and the "project" argument
isn't optional.

Instead of flushing the behind/ahead counts for all branches upon every
push we now only flush the cache of branches that actually need to have
these statistics recalculated. There are now basically 2 scenarios and
their effects:

1. A user pushes a commit to the default branch, this results in the
   cache being flushed for all branches.
2. A user pushes to a non default branch, this results in _only_ the
   cache for that branch being flushed.

The existing code (Repository#expire_cache) remains backwards compatible
with the previous behaviour, the new behaviour is only applied when a
branch name is passed as an argument. This ensures that when for example
a project is deleted the cache for all branches is flushed.

This caches the output of the following methods:

* Repository#empty?
* Repository#has_visible_content?
* Repository#root_ref

The cache for Repository#has_visible_content? is flushed whenever a
commit is pushed to a new branch or an existing branch is removed.
The cache for Repository#root_ref is only flushed whenever a user
changes the default branch of a project. The cache for Repository#empty?
is never explicitly flushed as there's no need for it.

gitlab_git 8.1 adds the ability to count the amount of commits between
two references without having to allocate anything but regular
Rugged::Commit objects. This in turn speeds up the process of counting
the number of commits a branch is ahead/behind by about 3.5x.

Leaving out the -I option in "git grep" would cause an Error 500 because the
resulting line would include "Binary file X matches"

Gitlab::Git::Repository#branch_count is a tad faster than the previous
setup. See gitlab-org/gitlab_git!62 for more information.

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Using the fuzzy filter, develop "file finder" feature.
- feedback(http://feedback.gitlab.com/forums/176466-general/suggestions/4987909-add-file-finder-fuzzy-input-in-files-tab-to-ju )
- fuzzy filter(https://github.com/jeancroy/fuzzaldrin-plus)
- shortcuts(when "t" was hitted at tree view, go to 'file find' page and 'esc' is to go back)
- depends on gitlab_git 7.2.22