Ensure syntax errors and other configuration problems are surfaced to the user.

Summary:
Some PHP has junky defaults for error_reporting / display_errors, and the "@"
silences fatals. The @ should never have been there, I just copied it from the
libphutil initializer where we use @ because the default error message can be
confusing and we display a more useful one.

Test Plan:
Added fatals to my conf file, got a decent error message instead of silent exit
with err=255.

Reviewed By: aran
Reviewers: tuomaspelkonen, aran, jungejason
CC: aran
Differential Revision: 355