Fix PHP version check for function calls with static/variable functions

Summary: D10132 improved this check by eliminating some false postives, but assumes an n_FUNCTION_CALL always starts with n_SYMBOL_NAME. This is true for f(), but not true for C::m() or $v().

Test Plan: Added and ran unit tests.

Reviewers: btrahan, joshuaspence

Reviewed By: joshuaspence

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D10467