Use semantic versioning for XHPAST
Summary: Currently XHPAST is versioned as x.y.z/w which seems a little odd. Instead, use x.y.z as the version number to make it possible to use version_compare.
Test Plan: N/A
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Subscribers: Korvin
Differential Revision: https://secure.phabricator.com/D13960