git gui: keep selected branch when remote is changed in push dialog

The selection of the branch to be pushed would be cleared when
the remote was changed. This seems to be dependent on the fact that
the selected content in the combobox was exported to the clipboard. It
was only apparent when using the new ttk widget.

Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>

lib/transport.tcl

@@ -135,7 +135,9 @@ proc do_push_anywhere {} {
 			-value remote \
 			-variable push_urltype
 		if {$use_ttk} {
-			ttk::combobox $w.dest.remote_m -textvariable push_remote \
+			ttk::combobox $w.dest.remote_m -state readonly \
+				-exportselection false \
+				-textvariable push_remote \
 				-values $all_remotes
 		} else {
 			eval tk_optionMenu $w.dest.remote_m push_remote $all_remotes