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.
 
diff --git a/lib/diff.tcl b/lib/diff.tcl
index 4a7138b..14a479f 100644
--- a/lib/diff.tcl
+++ b/lib/diff.tcl
@@ -166,7 +166,7 @@
 		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
diff --git a/lib/index.tcl b/lib/index.tcl
index d011406..b045219 100644
--- a/lib/index.tcl
+++ b/lib/index.tcl
@@ -164,6 +164,7 @@
 		_O -
 		AM {set new A_}
 		_T {set new T_}
+		_U -
 		U? {
 			if {[file exists $path]} {
 				set new M_