src: rename ASSERT macros in node_crypto.cc

Rename the misnomers ASSERT_IS_STRING_OR_BUFFER and ASSERT_IS_BUFFER.
Said macros don't assert, they throw a TypeError and return.

PR-URL: https://github.com/iojs/io.js/pull/529


Reviewed-By: Trevor Norris <trev.norris@gmail.com>