* netrc.el: Autoload encrypt when encrypt-file-alist is set.

* netrc.el: Autoload encrypt when encrypt-file-alist is set.
(netrc-parse): Use encrypt-file-alist to determine if
encrypt-find-model or encrypt-insert-file-contents should be used.

* encrypt.el: Clarify documentation.  Load password-cache or
password, whichever one is found first, instead of autoloading.