git-gui: Enhance choose_rev to handle hundreds of branches

One of my production repositories has hundreds of remote tracking
branches.  Trying to navigate these through a popup menu is just
not possible.  The list is far larger than the screen and it does
not scroll fast enough to efficiently select a branch name when
trying to create a branch or delete a branch.

This is major rewrite of the revision chooser mega-widget.  We
now use a single listbox for all three major types of named refs
(heads, tracking branches, tags) and a radio button group to pick
which of those namespaces should be shown in the listbox.  A filter
field is shown to the right allowing the end-user to key in a glob
specification to filter the list they are viewing.  The filter is
always taken as substring, so we assume * both starts and ends the
pattern the user wanted but otherwise treat it as a glob pattern.

This new picker works out really nicely.  What used to take me at
least a minute to find and select a branch now takes mere seconds.

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

lib/branch_create.tcl

@@ -63,7 +63,7 @@ constructor dialog {} {
 	pack $w.desc -anchor nw -fill x -pady 5 -padx 5
 
 	set w_rev [::choose_rev::new $w.rev {Starting Revision}]
-	pack $w.rev -anchor nw -fill x -pady 5 -padx 5
+	pack $w.rev -anchor nw -fill both -expand 1 -pady 5 -padx 5
 
 	labelframe $w.options -text {Options}
 
@@ -170,13 +170,7 @@ method _create {} {
 		return
 	}
 
-	if {[catch {set new [$w_rev get_commit]}]} {
-		tk_messageBox \
-			-icon error \
-			-type ok \
-			-title [wm title $w] \
-			-parent $w \
-			-message "Invalid revision: [$w_rev get]"
+	if {[catch {set new [$w_rev commit_or_die]}]} {
 		return
 	}