stash pop: remove 'apply' options during 'drop' invocation

stash pop: remove 'apply' options during 'drop' invocation

The 'git stash pop' option parsing used to remove the first argument
in --index mode.  At the time this was implemented, this first
argument was always --index.  However, since the invention of the -q
option in fcdd0e9 (stash: teach quiet option, 2009-06-17) you can
cause an internal invocation of

  git stash drop --index

by running

  git stash pop -q --index

which then of course fails because drop doesn't know --index.

To handle this, instead let 'git stash apply' decide what the future
argument to 'drop' should be.

Warning: this means that 'git stash apply' must parse all options that
'drop' can take, and deal with them in the same way.  This is
currently true for its only option -q.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Acked-by: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>