git-gui: Use a smaller pipe buffer for update-index.

When we shove a large number of files at update-index and they have
very short path names we are likely going to fit a large number of
them into the pipe buffer very early; thereby seeing a huge progress
update followed by lots of waiting between progress updates due to
the latency of update-index.

Using a smaller buffer should help smooth out the progress updates
as we are better able to keep tabs on the update-index process'
progress through our list of paths.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui

@@ -1171,7 +1171,11 @@ proc update_index {pathList} {
 		$totalCnt \
 		0.0]
 	set fd [open "| git update-index --add --remove -z --stdin" w]
-	fconfigure $fd -blocking 0 -translation binary
+	fconfigure $fd \
+		-blocking 0 \
+		-buffering full \
+		-buffersize 512 \
+		-translation binary
 	fileevent $fd writable [list \
 		write_update_index \
 		$fd \