Kill the blame back-end on window close.

Currently 'git-gui blame' does not kill its back-end
process, hoping that it will die anyway when the pipe
is closed. However, in some cases the process works
for a long time without producing any output. This
behavior results in a runaway CPU hog.

Signed-off-by: Alexander Gavrilov <angavrilov@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -497,6 +497,20 @@ proc githook_read {hook_name args} {
 	return {}
 }
 
+proc kill_file_process {fd} {
+	set process [pid $fd]
+
+	catch {
+		if {[is_Windows]} {
+			# Use a Cygwin-specific flag to allow killing
+			# native Windows processes
+			exec kill -f $process
+		} else {
+			exec kill $process
+		}
+	}
+}
+
 proc sq {value} {
 	regsub -all ' $value "'\\''" value
 	return "'$value'"