Remove (most of) error suppression from database drivers (issue #3036)
Call data_seek(0) only if we've used DB_result::*row*() methods

This should fix HHVM where it throws 'Unable to jump to row 0 on MySQL result index X' error messages for ext/mysqli
Add hash_equals() to ext/hash compat layer

Introduced in PHP 5.6 Beta 1 (unfortunately, still undocumented).
RFC: https://wiki.php.net/rfc/timing_attack

(Yes, I am aware that the RFC talks about hash_compare(), the function was later renamed in the implementation.)
Fix PHP 5.6 charset-related warnings in tests
Suppress PHP 5.6 E_DEPRECATED warnings for mbstring.internal_encoding as well