Add pcntl_sigprocmask

Summary: fixes facebook/hhvm#4160

pthread_sigprocmask seems most correct given HHVM's model, however for both PHP-FastCGI and HHVM, the mask will leak cross-request

Reviewed By: @paulbiss

Differential Revision: D1667740

Signature: t1:1667740:1415399505:d7edad8e22ba9c8063800c98adf284ffe886f360
Use Func::destroy to clean up elements of the pseudomain cache

Summary: Funcs in the pseudomain cache are allocated by clone -- it seems like
they should be deallocated by destroy, rather than just deleted.  (ASAN
complains about the mismatch between malloc'ing the Func and deleting it.)

Reviewed By: @markw65

Differential Revision: D1668805

Signature: t1:1668805:1415417063:efd7495176f15d82660cd10037d5a0d54b52588c