CVS tags are officially only allowed to use [-_0-9A-Za-f]. Git
refs commonly uses other characters, especially [./]. Such characters
need to be escaped from CVS in order to be referenced.
This just defines functions to escape/unescape names. The functions
are not used yet.
Signed-off-by: Matthew Ogilvie <mmogilvi_git@miniinfo.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>