git-gui: Do not automatically stage file after merge tool finishes

If a merge tool was invoked on a conflicted file and the tool completed,
then the conflicted file was staged automatically. However, the fact that
the user closed the merge tool cannot be understood as the unequivocal
sign that the conflict was completely resolved. For example, the user
could have decided to postpone the resolution of the conflict, or could
have accidentally closed the tool. We better leave the file unstaged and
let the user stage it explicitly.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

lib/mergetool.tcl

@@ -375,14 +375,6 @@ proc merge_tool_finish {fd} {
 		}
 	}
 
-	# Check the modification time of the target file
-	if {!$failed && [file mtime $mtool_target] eq $mtool_mtime} {
-		if {[ask_popup [mc "File %s unchanged, still accept as resolved?" \
-				[short_path $mtool_target]]] ne {yes}} {
-			set failed 1
-		}
-	}
-
 	# Finish
 	if {$failed} {
 		file rename -force -- $backup $mtool_target
@@ -395,6 +387,6 @@ proc merge_tool_finish {fd} {
 
 		delete_temp_files $mtool_tmpfiles
 
-		merge_add_resolution $mtool_target
+		reshow_diff
 	}
 }