Unicode file name support (gitk and git-gui)
Assumes file names in git tree objects are UTF-8 encoded.
On most unix systems, the system encoding (and thus the TCL system
encoding) will be UTF-8, so file names will be displayed correctly.
On Windows, it is impossible to set the system encoding to UTF-8. Changing
the TCL system encoding (via 'encoding system ...', e.g. in the startup
code) is explicitly discouraged by the TCL docs.
Change gitk and git-gui functions dealing with file names to always convert
from and to UTF-8.
Signed-off-by: Karsten Blees <blees@dcon.de>