Rename _ssh_sock() to fix code style issue.

Since _ssh_sock is imported out of the git_command module, the leading
underscore should be removed from the function name.
diff --git a/git_command.py b/git_command.py
index d56ad0a..3309f37 100644
--- a/git_command.py
+++ b/git_command.py
@@ -30,7 +30,7 @@
 _ssh_proxy_path = None
 _ssh_sock_path = None
 
-def _ssh_sock(create=True):
+def ssh_sock(create=True):
   global _ssh_sock_path
   if _ssh_sock_path is None:
     if not create:
@@ -119,7 +119,7 @@
     if disable_editor:
       env['GIT_EDITOR'] = ':'
     if ssh_proxy:
-      env['REPO_SSH_SOCK'] = _ssh_sock()
+      env['REPO_SSH_SOCK'] = ssh_sock()
       env['GIT_SSH'] = _ssh_proxy()
 
     if project: