crypto: support passwords in publicEncrypt

Private keys may be used along with publicEncrypt since the private key
includes the public one.  This adds the ability to use encrypted private
keys which previously threw an error.  This commit also makes sure the
user exposed functions have names.

PR-URL: https://github.com/iojs/io.js/pull/626


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>