Revert "Fix for bad_shell_exec failing depending on the user's shell"

Summary: This reverts commit 62eb6be5d23126089f8c2619da976d7f23550a71.

Reviewed By: @ptarjan

Differential Revision: D1423366
Fix casting a DateTime to an array

Summary: Fixes facebook/hhvm#3083

Reviewed By: @ptarjan

Differential Revision: D1414803
Make SplHeap comparisons work on non-number objects

Summary: `compare()` only gets called with comparison to greater than zero. I could change it to return true if is greater than. Keeping the same behaviour matches the name

Fixes #3086
Closes #3091

Reviewed By: @ptarjan

Differential Revision: D1422402

Pulled By: @fredemmott