git-gui: Request blame metadata in utf-8.

The blame builtin now supports automatic conversion of
metadata encoding. By default it is converted to the
character set specified by i18n.logoutputencoding.

Since gui blame expects the data in utf-8, it is
necessary to specify the desired encoding directly.
An old version of the blame command will simply
ignore the option.

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

lib/blame.tcl

@@ -559,7 +559,7 @@ method _read_file {fd jump} {
 } ifdeleted { catch {close $fd} }
 
 method _exec_blame {cur_w cur_d options cur_s} {
-	lappend options --incremental
+	lappend options --incremental --encoding=utf-8
 	if {$commit eq {}} {
 		lappend options --contents $path
 	} else {