git-gui: Honor core.excludesfile when listing extra files

Recent git versions have a git-status that honors the core.excludesfile
configuration option when it reports on untracked files.  Unfortunately
I missed the introduction of this configuration option in the core
porcelain implementation, so it was not reflected here in git-gui.

Found and reported by Lars Noschinski <lars@public.noschinski.de>.

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

git-gui.sh

@@ -872,6 +872,10 @@ proc rescan_stage2 {fd after} {
 	if {[file readable $info_exclude]} {
 		lappend ls_others "--exclude-from=$info_exclude"
 	}
+	set user_exclude [get_config core.excludesfile]
+	if {$user_exclude ne {} && [file readable $user_exclude]} {
+		lappend ls_others "--exclude-from=$user_exclude"
+	}
 
 	set buf_rdi {}
 	set buf_rdf {}