Fix two issues with shell/config scripts for hosted repositories

Summary: Ref T4151. `-ne` is numeric in some/most/all shells; `exec --` apparently doens't always work.

Test Plan: Will make @zeeg test.

Reviewers: btrahan, zeeg

Reviewed By: zeeg

CC: zeeg, aran

Maniphest Tasks: T4151

Differential Revision: https://secure.phabricator.com/D7702