git-gui: don't warn for detached head when rebasing

Signed-off-by: Bert Wesarg <bert.wesarg@googlemail.com>
Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>
diff --git a/lib/commit.tcl b/lib/commit.tcl
index e27e148..0d81432 100644
--- a/lib/commit.tcl
+++ b/lib/commit.tcl
@@ -263,7 +263,9 @@
 	global is_detached repo_config
 	global pch_error
 
-	if {$is_detached && [is_config_true gui.warndetachedcommit]} {
+	if {$is_detached
+	    && ![file exists [gitdir rebase-merge head-name]]
+	    && 	[is_config_true gui.warndetachedcommit]} {
 		set msg [mc "You are about to commit on a detached head.\
 This is a potentially dangerous thing to do because if you switch\
 to another branch you will loose your changes and it can be difficult\