git-gui: Misc. bug fixes for mouse click crashes.

git-gui: Misc. bug fixes for mouse click crashes.

Make sure the file_lists array has both elements set at all times,
otherwise we get Tcl errors during mouse clicks in the file list
areas due to the list not being defined.

Also added M1-A as a keyboard binding within the console window
text area.  This lets users select all text easily and copy it
to the clipboard.

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