git-p4: move to toplevel

Move git-p4 out of contrib/fast-import into the main code base,
aside other foreign SCM tools.

Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/INSTALL b/INSTALL
index 58b2b86..87e03bb 100644
--- a/INSTALL
+++ b/INSTALL
@@ -131,6 +131,9 @@
 	  use English. Under autoconf the configure script will do this
 	  automatically if it can't find libintl on the system.
 
+	- Python version 2.6 or later is needed to use the git-p4
+	  interface to Perforce.
+
  - Some platform specific issues are dealt with Makefile rules,
    but depending on your specific installation, you may not
    have all the libraries/tools needed, or you may have