Summary:
Create an extension that allows shell variables to be passed to the
server via command line option. When pushing with the following command:
hg push --pushvars "DEBUG=1"
will make HG_SCM_DEBUG=1 available to the hooks. Note the prepending of HG_SCM_
Test Plan: Run run_tests
Reviewers: pyd, rmcelroy, durham
Reviewed By: durham
Differential Revision: https://phabricator.fb.com/D1991994
Tasks: 4841351
Signature: t1:1991994:1430417209:9a05fb11f9ecdeab3a1d89cf331014dafe7d959f
