Port WarmupRequestHandler fixes to rc branch

Reviewed By: @markw65

Differential Revision: D1664573
Stack overflow in KernelVersion parser

Summary: Caught by ASAN

Reviewed By: @ottoni

Differential Revision: D1651562

Signature: t1:1651562:1414731602:574aa61ef4b4538f26299f6694aff3c5e3bc317d
Delete (instead of free) Class::m_extra

Summary: It's allocated by new, so we should probably be symmetric.

Reviewed By: @mxw

Differential Revision: D1655737

Signature: t1:1655737:1415049149:c4ce71784fc9f6aed1a962f026a7d39c75a603ce
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