This function was added in PHP 5.4.0 and can be used now that MediaWiki
only works with PHP 5.5.9 or higher.
Also fixed a bug in ApiQueryCategoryMembers::validateHexSortkey() that
allowed a single line feed at the end of the string to pass.
Change-Id: I5b577e7dcc5fb6a06ab550429aae657dbcc79083
MWCryptRand already has some useful utility functions wrapping PHP's
hash() and hash_hmac(). Let's make them public so we can use them from
other code.
But since "MWCryptRand" isn't really a good place for hashing functions,
let's move them to "MWCryptHash" instead.
Change-Id: I7542c719ac72beba7b0f6aa170bdb4c69fa6beab
