gitk: Synchronize highlighting in file view for 'f' and 'b' commands

This is based on a patch by Eric Raible <raible@gmail.com>, but does
things a bit more simply.

Previously, 'b', backspace, and delete all did the same thing.
This changes 'b' to perform the inverse of 'f'.  And both of
them now highlight the filename of the currently diff.

This makes it easier to review and navigate the diffs associated
with a particular commit using only f, b, and space because the
filename of the currently display diff will be dynamically
highlighted.

Signed-off-by: Paul Mackerras <paulus@samba.org>

gitk

@@ -1016,7 +1016,7 @@ proc makewindow {} {
     bindkey k "selnextline 1"
     bindkey j "goback"
     bindkey l "goforw"
-    bindkey b "$ctext yview scroll -1 pages"
+    bindkey b prevfile
     bindkey d "$ctext yview scroll 18 units"
     bindkey u "$ctext yview scroll -18 units"
     bindkey / {dofind 1 1}
@@ -5479,26 +5479,44 @@ proc changediffdisp {} {
     $ctext tag conf d1 -elide [lindex $diffelide 1]
 }
 
+proc highlightfile {loc cline} {
+    global ctext cflist cflist_top
+
+    $ctext yview $loc
+    $cflist tag remove highlight $cflist_top.0 "$cflist_top.0 lineend"
+    $cflist tag add highlight $cline.0 "$cline.0 lineend"
+    $cflist see $cline.0
+    set cflist_top $cline
+}
+
 proc prevfile {} {
-    global difffilestart ctext
-    set prev [lindex $difffilestart 0]
+    global difffilestart ctext cmitmode
+
+    if {$cmitmode eq "tree"} return
+    set prev 0.0
+    set prevline 1
     set here [$ctext index @0,0]
     foreach loc $difffilestart {
 	if {[$ctext compare $loc >= $here]} {
-	    $ctext yview $prev
+	    highlightfile $prev $prevline
 	    return
 	}
 	set prev $loc
+	incr prevline
     }
-    $ctext yview $prev
+    highlightfile $prev $prevline
 }
 
 proc nextfile {} {
-    global difffilestart ctext
+    global difffilestart ctext cmitmode
+
+    if {$cmitmode eq "tree"} return
     set here [$ctext index @0,0]
+    set line 1
     foreach loc $difffilestart {
+	incr line
 	if {[$ctext compare $loc > $here]} {
-	    $ctext yview $loc
+	    highlightfile $loc $line
 	    return
 	}
     }