Add sync-c option to manifest

There are use-cases when fetching all branch is impractical and
we really need to fetch only one branch/tag.
e.g. there is a large project with binaries and every update of a
binary file is put to a separate branch.
The whole project history might be too large to allow users fetch it.

Add 'sync-c' option to 'project' and 'default' tags to make it possible
to configure 'sync-c' behavior at per-project and per-manifest level.

Note that currently there is no possibility to revert boolean flag from
command line. If 'sync-c' is set in manifest then you cannot make
full fetch by providing a repo tool argument.

Change-Id: Ie36fe5737304930493740370239403986590f593

project.py

@@ -510,7 +510,8 @@ class Project(object):
                revisionExpr,
                revisionId,
                rebase = True,
-               groups = None):
+               groups = None,
+               sync_c = False):
     self.manifest = manifest
     self.name = name
     self.remote = remote
@@ -531,6 +532,7 @@ class Project(object):
 
     self.rebase = rebase
     self.groups = groups
+    self.sync_c = sync_c
 
     self.snapshots = {}
     self.copyfiles = []
@@ -964,6 +966,7 @@ class Project(object):
     and self._ApplyCloneBundle(initial=is_new, quiet=quiet):
       is_new = False
 
+    current_branch_only = current_branch_only or self.sync_c or self.manifest.default.sync_c
     if not self._RemoteFetch(initial=is_new, quiet=quiet, alt_dir=alt_dir,
                              current_branch_only=current_branch_only):
       return False