gitk: Provide a window icon if possible
gitk: Provide a window icon if possible

Try to set up a 16x16 Tk photo image (based on the git logo) and use
it as window icon.  The code is wrapped in a catch because it may fail
in earlier Tcl/Tk 8.4 releases that don't provide 'wm iconphoto'.

Signed-off-by: Giuseppe Bilotta <6010d7f2c049984f25cd19568d4ace2cc46b0817@gmail.com>
Signed-off-by: Stephen Boyd <66c4b3fccf5786e0c6198a1e0f640664da3951b2@gmail.com>
Signed-off-by: Paul Mackerras <19a0ba370c443ba08d20b5061586430ab449ee8c@samba.org>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git