[PATCH] gitk: Enable selected patch text on Windows

[PATCH] gitk: Enable selected patch text on Windows

On windows, mouse input follows the keyboard focus, so to allow selecting
text from the patch canvas we must not shift focus back to the top level.
This change has no negative impact on X, so we don't explicitly test
for Win32 on this change. This provides similar selection capability
as already available using X-Windows.

Signed-off-by: Mark Levedahl <mdl123@verizon.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>