Detect and fatal on magic_quotes_gpc

Summary:
This is evil, don't run with it enabled. Somehow got enabled on my
laptop?

Test Plan:
Loaded phabricator with magic_quotes_gpc enabled, was rebuffed.

Reviewed By: aran
Reviewers: jungejason, tuomaspelkonen, aran
CC: aran
Differential Revision: 184