Fix a couple of problems that crept into mount

Fix a couple of problems that crept into mount

Commit 6facb22402a0bd8cd49be2ed1a0856b24fef42f4 changed the allocation
of len to no longer get 20 extra bytes.  It needs to get at least one
extra byte for a null character, otherwise a single extra option such
as "sec=krb5" is never copied in parse_opt() and is dropped.

Commit 44a3727a3243e674a1f1fdad5cbbc639aa25d01c added a typo when
checking the program name.

Signed-off-by: Neil Brown <neilb@suse.de>