Remove duplicately named variables from a closure class

Remove it from the usevar list. Also, add assert to catch stack pointer bugs.
Fastpath for simple array IssetM

TranslatorX64 has a fast path for this case so I thought I'd
try it out in the ir. It's a small but apparently real win in Perflab.
Remove special cases for vector instructions in the ir

VectorTranslator is now good enough that all of this code can be
removed without causing a perf regression. Instructions, loads, and stores are
all slightly up, but CPU time looks like noise.
Early release of m_received value

Continuation::send() uses m_received field to transfer the value inside
the continuation. This field remains set until the continuation is
iterated the next time.

Unset this field early by ContReceive so that the memory can be
reclaimed.
Split up ConvToDbl into sub-opcodes.

Split up ConvToDbl into ConvArrToDbl, ConvBoolToDbl, ConvIntToDbl,
ConvObjToDbl, ConvStrToDbl and ConvGenToDbl, so that different flags
can be set for each instruction.
Consolidate ContDone into ContRetC

Merge ContDone+ContExit into ContRetC with added support of passing results. This variable passing mechanism is not exposed to the PHP as the ReturnStatements in generators do not contain result expression. However, this is exposed by restored hphp_continuation_done() built-in to allow experimentation.

The idea is that once we introduce ContYield opcode (merge of all opcodes used by YieldExpression), we could change ContRetC and ContYield to leave result and done-status on the stack and leave it up to the caller (ContNext/ContSend/ContRaise) to fill in Continuation fields. This will make these opcodes more generic and useful for other things, while allowing us to move some properties to the VM and kill opcodes like ContCurrent.
Remove markCurrentAs{Succeeded,TailCall}

Tail calls were eliminated, results are set thru ContRetC opcode, these
functions are no longer needed.
Move some cold stubs from a to astubs

Bertrand's profiling data showed we're wasting the first 3
cache lines of a.  Move defClsHelper and the (now rarely used)
non-generic decref stubs to astubs.  Also adds some tracing I was
using to see how big and where things are.
Switch to reentrant safe calls in posix

posix_getpwuid()
posix_getpwnam()
posix_getgrgid()
posix_getgrnam()
posix_ttyname()

were using non-threadsafe posix calls.
Most using AttachLiteral for shared space as well.
Cleanup Static{Result,Exception}WaitHandle construction interfaces

Provide a Static{Result,Exception}WaitHandle::Create() static method for
internal use, use it by GenArrayWaitHandle.

Avoids one inc/decref (Array -> Variant -> m_resultOrException) if
GenArray received an array of finished dependencies.
Fix TestServer/TestXboxServer

A recent change to xbox makes it reset after every request.
This broke a test which was testing that threads only get
reset when they ask to be reset.