gitk: Fix file highlight when run in subdirectory

The "highlight this only" and "highlight this too" commands in gitk
add the path relative to $GIT_WORK_TREE to the "Find" input box. When
the search (using git-diff-tree) is run, the paths are used
unmodified, except for some shell escaping. Since the search is run
from gitk's working directory, no commits matching the paths will be
found if gitk was started in a subdirectory.

Make the paths passed to git-diff-tree relative to gitk's working
directory instead of being relative to $GIT_WORK_TREE. If, however,
gitk is run outside of the working directory (e.g. with $GIT_WORK_TREE
set), we still need to use the path relative to $GIT_WORK_TREE.

Signed-off-by: Martin von Zweigbergk <martin.von.zweigbergk@gmail.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

gitk

@@ -4527,12 +4527,17 @@ proc makepatterns {l} {
 
 proc do_file_hl {serial} {
     global highlight_files filehighlight highlight_paths gdttype fhl_list
+    global cdup
 
     if {$gdttype eq [mc "touching paths:"]} {
 	if {[catch {set paths [shellsplit $highlight_files]}]} return
 	set highlight_paths [makepatterns $paths]
 	highlight_filelist
-	set gdtargs [concat -- $paths]
+	set relative_paths {}
+	foreach path $paths {
+	    lappend relative_paths [file join $cdup $path]
+	}
+	set gdtargs [concat -- $relative_paths]
     } elseif {$gdttype eq [mc "adding/removing string:"]} {
 	set gdtargs [list "-S$highlight_files"]
     } else {
@@ -11641,6 +11646,10 @@ set stuffsaved 0
 set patchnum 0
 set lserial 0
 set isworktree [expr {[exec git rev-parse --is-inside-work-tree] == "true"}]
+set cdup {}
+if {$isworktree} {
+    set cdup [exec git rev-parse --show-cdup]
+}
 setcoords
 makewindow
 catch {