git-gui: Combine blame groups only if commit and filename match

Consecutive chunks of a file could come from the same commit, but
have different original file names.  Previously we would have put
them into a single group, but then the hyperlink would jump to only
one of the files, and the other would not be accessible.  Now we can
get to the other file too.

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

lib/blame.tcl

@@ -518,8 +518,10 @@ method _read_blame {fd} {
 
 			set first_lno $lno
 			while {
-			![catch {set ncmit $line_commit([expr {$first_lno - 1}])}]
+			   ![catch {set ncmit $line_commit([expr {$first_lno - 1}])}]
+			&& ![catch {set nfile $line_file([expr {$first_lno - 1}])}]
 			&& $ncmit eq $cmit
+			&& $nfile eq $file
 			} {
 				incr first_lno -1
 			}
@@ -572,8 +574,12 @@ method _read_blame {fd} {
 				incr blame_lines
 			}
 
-			while {![catch {set ncmit $line_commit($lno)}]
-				&& $ncmit eq $cmit} {
+			while {
+			   ![catch {set ncmit $line_commit($lno)}]
+			&& ![catch {set nfile $line_file($lno)}]
+			&& $ncmit eq $cmit
+			&& $nfile eq $file
+			} {
 				$w_cgrp delete $lno.0 "$lno.0 lineend"
 
 				if {$lno == $first_lno} {