Add GitcClientCommand class for GITC-specific commands

These won't show up as common commands in the help text unless in a GITC
client, and will refuse to execute.

Change-Id: Iffe82adcc9d6ddde9cb4b204f83ff018042bdab0
diff --git a/subcmds/gitc_init.py b/subcmds/gitc_init.py
index c243bb3..4f9d734 100644
--- a/subcmds/gitc_init.py
+++ b/subcmds/gitc_init.py
@@ -18,12 +18,12 @@
 import sys
 
 import gitc_utils
-from command import RequiresGitcCommand
+from command import GitcAvailableCommand
 from manifest_xml import GitcManifest
 from subcmds import init
 
 
-class GitcInit(init.Init, RequiresGitcCommand):
+class GitcInit(init.Init, GitcAvailableCommand):
   common = True
   helpSummary = "Initialize a GITC Client."
   helpUsage = """