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>

lib/diff.tcl

@@ -166,7 +166,7 @@ proc show_diff {path w {lno {}} {scroll_pos {}}} {
 		lappend cmd diff-index
 		lappend cmd --cached
 	} elseif {$w eq $ui_workdir} {
-		if {[string index $m 0] eq {U}} {
+		if {[string first {U} $m] >= 0} {
 			lappend cmd diff
 		} else {
 			lappend cmd diff-files