options flags:
~~~~~~~~~~~~~
  PARSE_OPT_NONEG allow the caller to disallow the negated option to exists.

option types:
~~~~~~~~~~~~
  OPTION_BIT: ORs (or NANDs) a mask.
  OPTION_SET_INT: force the value to be set to this integer.
  OPTION_SET_PTR: force the value to be set to this pointer.

helper:
~~~~~~
  HAS_MULTI_BITS (in git-compat-util.h) is a bit-hack to check if an
  unsigned integer has more than one bit set, useful to check if conflicting
  options have been used.
Signed-off-by: NPierre Habouzit <madcoder@debian.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>