set errno = EINVAL for invalid salts and hashes in most functions.

set errno = EINVAL for invalid salts and hashes in most functions.
remember to set EACCES in bcrypt_checkpass for hash differences.
the higher level crypt_checkpass function will reset errno to EACCES in
all cases, which is probably the right behavior, but this change gives code
working with the lower level functions the correct errno if they care.