Merge branch 'ib/scripted-parse-opt-better-hint-string' into maint

The "rev-parse --parseopt" mode parsed the option specification
and the argument hint in a strange way to allow '=' and other
special characters in the option name while forbidding them from
the argument hint.  This made it impossible to define an option
like "--pair <key>=<value>" with "pair=key=value" specification,
which instead would have defined a "--pair=key <value>" option.

* ib/scripted-parse-opt-better-hint-string:
  rev-parse --parseopt: allow [*=?!] in argument hints