diff: align move detection error handling with other options

diff: align move detection error handling with other options

This changes the error handling for the options --color-moved-ws
and --color-moved-ws to be like the rest of the options.

Move the die() call out of parse_color_moved_ws into the parsing
of command line options. As the function returns a bit field, change
its signature to return an unsigned instead of an int; add a new bit
to signal errors. Once the error is signaled, we discard the other
bits, such that it doesn't matter if the error bit overlaps with any
other bit.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>