Allow --3way to be passed to `git apply` via `git cl patch`.

git_cl.py

Index: git_cl.py
diff --git a/git_cl.py b/git_cl.py
index 01fe0767afdb4691e94a121b001e30d50b2239ba..082b4ebff80196f73684b3b512a2f09691f1e5ad 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -1692,7 +1692,8 @@ def CMDpatch(parser, args):
   parser.add_option('-f', action='store_true', dest='force',
                     help='with -b, clobber any existing branch')
   parser.add_option('--reject', action='store_true', dest='reject',
-                    help='allow failed patches and spew .rej files')
+                    help='failed patches spew .rej files rather than '
+                        'attempting a 3-way merge')
   parser.add_option('-n', '--no-commit', action='store_true', dest='nocommit',
                     help="don't commit after patch applies")
   (options, args) = parser.parse_args(args)
@@ -1750,6 +1751,8 @@ def CMDpatch(parser, args):
   cmd = ['git', '--no-pager', 'apply', '--index', '-p0']
   if options.reject:
     cmd.append('--reject')
+  else:
+    cmd.append('--3way')

[ncarter (slow), 2013/06/07 19:42:00]

FYI: this option doesn't seem to exist in git version 1.7.9.6, which I think is
the version that seems to be on many macs (somebody claimed it gets installed
with xcode). Do we have a minimum git version?

[M-A Ruel, 2013/06/07 19:44:45]

Trent, can you revert or fix? We have to support somewhat older versions to a
certain extent.

   try:
     subprocess2.check_call(cmd, stdin=patch_data, stdout=subprocess2.VOID)
   except subprocess2.CalledProcessError: