Relevant BUGIDs: 521314

Relevant BUGIDs: 521314

Purpose of commit: bugfix

Commit summary:
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bigcrypt does not match crypt when password length is too long.
This led to a pam_unix problem when the module had not set the
password in bigcrypt mode, but was trying to compare with bigcrypt
output. The fix is to use the stored password as a guide to how much
of the encrypted password to compare against.