git-gui: Support conflict states _U & UT.

Support _U (local deleted, remote modified) and
UT (file type changed in conflict) modes.

Note that 'file type changed' does not refer to
changes in the executable bit, instead it denotes
replacing a file with a link, or vice versa.

Signed-off-by: Alexander Gavrilov <angavrilov@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
diff --git a/lib/commit.tcl b/lib/commit.tcl
index f4ab707..2977315 100644
--- a/lib/commit.tcl
+++ b/lib/commit.tcl
@@ -151,6 +151,7 @@
 		D? -
 		T_ -
 		M? {set files_ready 1}
+		_U -
 		U? {
 			error_popup [mc "Unmerged files cannot be committed.