Remove spurious parentheses from VIPRestrictedCommands[Check|Test]
Move check for WP_User_Query to a class and file of its own

Moving it out of VIPRestrictedCommandsCheck is a preparatory step
for using PHP-Parser for checks, as all the other checks in
VIPRestrictedCommandsCheck are for function calls, not classes.
Add a test for VIPRestrictedClassesCheck
Merge pull request #217 from ockham/vip-restricted-commands-check-fixes

Refactor VIPRestrictedCommands checks & tests