repo: Support multiple branches for the same project.

It is often useful to be able to include the same project more than
once, but with different branches and placed in different paths in the
workspace. Add this feature.

This CL adds the concept of an object directory. The object directory
stores objects that can be shared amongst several working trees. For
newly synced repositories, we set up the git repo now to share its
objects with an object repo.

Each worktree for a given repo shares objects, but has an independent
set of references and branches. This ensures that repo only has to
update the objects once; however the references for each worktree are
updated separately. Storing the references separately is needed to
ensure that commits to a branch on one worktree will not change the
HEAD commits of the others.

One nice side effect of sharing objects between different worktrees is
that you can easily cherry-pick changes between the two worktrees
without needing to fetch them.

Bug: Issue 141
Change-Id: I5e2f4e1a7abb56f9d3f310fa6fd0c17019330ecd
Canonicalize project hooks path before use

If the top-level .repo directory is moved somewhere else (e.g. a
different drive) and replaced with a symlink, _InitHooks() will create
broken symlinks. Resolving symlinks before computing the relative path
for the symlink keeps the path within the repo tree, so the tree can
be moved anywhere.

Change-Id: Ifa5c07869e3477186ddd2c255c6c607f547bc1fe
Add --archive option to init to sync using git archive

This significantly reduces sync time and used brandwidth as only
a tar of each project's revision is checked out, but git is not
accessible from projects anymore.

This is relevant when git is not needed in projects but sync
speed/brandwidth may be important like on CI servers when building
several versions from scratch regularly for example.

Archive is not supported over http/https.

Change-Id: I48c3c7de2cd5a1faec33e295fcdafbc7807d0e4d
Signed-off-by: Julien Campergue <julien.campergue@parrot.com>
Fix error in xml manifest doc.

The docs on the annotations say that zero or more may exist as a child
of a project, so that means that a "*" instead of a "?" should be used.

Change-Id: Iff855d003dfb05cd980f285a237332914e1dad70
Don't backtrace when current branch is not uploadable.

The backtrace currently occurs when one uses the "--cbr" argument with
the repo upload subcommand if the current branch is not tracking an
upstream branch. There may be other cases that would backtrace as well,
but this is the only one I found so far.

Change-Id: Ie712fbb0ce3e7fe3b72769fca89cc4c0e3d2fce0
hooks/pre-auto-gc: fix AC detection on OSX Maverick

The output of pmset has been changed to "Now drawing from 'AC Power'"

Change-Id: Id425d3bcd6a28656736a6d2c3096623a3ec053cc
Merge "Add --archive option to init to sync using git archive"
Fix os.mkdir race condition.

This code checks whether a dir exists before creating it. In between the
check and the mkdir call, it is possible that another process will have
created the directory. We have seen this bug occur many times in
practice during our 'repo init' tests.

Change-Id: Ia47d39955739aa38fd303f4e90be7b4c50d9d4ba
Merge "Canonicalize project hooks path before use"
Merge "repo: Support multiple branches for the same project."
Merge "hooks/pre-auto-gc: fix AC detection on OSX Maverick"
Merge "Don't backtrace when current branch is not uploadable."
Only fetch current branch on shallow clients

Fetching a new branch on a shallow client may download the entire
project history, as the depth parameter is not passed to git
fetch. Force the fetch to only download the current branch.

Change-Id: Ie17ce8eb5e3487c24d90b2cae8227319dea482c8
Merge "Only fetch current branch on shallow clients"
Properly iterate through values

the value of Manifest.projects has changed from being the dictionary
to the values of the dictionary.  Here we handle this change
correctly on a PostRepoUpgrade.

From a `git diff v1.12.7 -- manifest_xml.py`:
+  @property
   def projects(self):
     self._Load()
-    return self._projects
+    return self._paths.values()

self._paths does contain the projects according to this line of
manifest_xml.py:
484      self._paths[project.relpath] = project

Change-Id: I141f8d5468ee10dfb08f99ba434004a307fed810
repo: Fix 'remove-project' regression with multiple projects.

In CL:50715, I updated repo to handle multiple projects, but the
remove-projects code path was not updated accordingly. Update it.

Change-Id: Icd681d45ce857467b584bca0d2fdcbf24ec6e8db
Handle release candidates in git version parsing

Right now repo chokes on git versions like "1.9.rc1".  This change
treats 'rc*' as a '0'.

Change-Id: I612b7b431675ba7415bf70640a673e48dbb00a90
Respect version hyphenation

The last change regarding version parsing lost handling of version
hyphenation, this restores that.  In otherwords,
1.1.1-otherstuff is parsed as (1,1,1) instead of (1,1,0)

Change-Id: I3753944e92095606653835ed2bd090b9301c7194
Add wrapper module

This takes the wrapper importing code from main.py and moves it into
its own module so that other modules may import it without causing
circular imports with main.py.

Change-Id: I9402950573933ed6f14ce0bfb600f74f32727705
Share git version parsing code with wrapper module

'repo' and 'git_command.py' had their own git version parsing code.
This change shares that code between the modules.  DRY is good.

Change-Id: Ic896d2dc08353644bd4ced57e15a91284d97d54a