Remove duplicate stack size code

Summary: We already had code forcing the stack size to 8M,
but recently added more code to force it to 8 in normal mode,
and 16 in ASAN mode.

In addition, the old code always ran, even if the main thread wasn't
going to do much real work (eg when running as a server).

Drop the old code in favor of the new.

Reviewed By: @edwinsmith

Differential Revision: D1683119

Signature: t1:1683119:1416055986:e7fecf294752fc6f2f17478f613919f46929eea2
Fix a bug in Index::lookup_constraint

Reviewed By: @paroski

Differential Revision: D1680897
Allow non-static expressions in function parameter defaults

Summary: This is primarily for HNI expressions such as the following
in datetime:

  function date(string $format, int $now = TimeStamp::Current());

HHVM compiles default arguments to Bytecode and jumps to the correct
location in the function for initialization anyway, so there's no real
need to limit the default to static expressions apart from PHP's
language design.

Closes #2886

Reviewed By: @paulbiss

Differential Revision: D1682957

Signature: t1:1682957:1416007027:42343f4baf80906e22308e1e1e91bea7027967d1
Fix Symfony's it's not safe to rely on system timezone setting errors

Summary: Symfony requires a date.timezone setting in the standard php.ini
We can't do that so this modification adds a call to date_default_timezone_set
Closes https://github.com/facebook/hhvm/pull/4251

Reviewed By: @fredemmott

Differential Revision: D1683075

Signature: t1:1683075:1416091145:b2eca865d5811e41aa0669519f59ac8dc5188341
Remove mostly-unused PreClass* field from PreClass::{Prop,Const}

Summary: It was only being used in their pretty-print methods, but those are only
called from PreClass::prettyPrint, so we can just pass the current PreClass*
over to them instead of having to store it.

Reviewed By: @bertmaher

Differential Revision: D1681944

Signature: t1:1681944:1415999560:911757507ea045d3c4e9cf0269aa9221b1f9ed8d