crypto: clear error on return in TLS methods
crypto: clear error on return in TLS methods

Methods like `X509_STORE_add_cert` may push errors onto OpenSSL's error
stack. Ensure that they won't pop up in a different places like
`tls_wrap.cc`.

Fix: https://github.com/iojs/io.js/issues/712
PR-URL: https://github.com/iojs/io.js/pull/719
Reviewed-By: Ben Noordhuis <59bd0a3ff43b32849b319e645d4798d8a5d1e889@bnoordhuis.nl>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node