git-p4: decode p4 wildcard characters

git-p4: decode p4 wildcard characters

There are four wildcard characters in p4.  Files with these
characters can be added to p4 repos using the "-f" option.
They are stored in %xx notation, and when checked out, p4
converts them back to normal.

This patch does the same thing when importing into git,
converting the four special characters.  Without this change,
the files appear with literal %xx in their names.

Be careful not to produce "*" in filenames on windows.  That
will fail.

Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>