Minor fix for typecast linter rule
Summary: intval($x, $y) cannot be safely changed to (int)$x if $y != 10.
Test Plan: Added test cases.
Reviewers: #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: Korvin
Differential Revision: https://secure.phabricator.com/D14611