More uses of range-for, and a couple other things.

Used range-for in more places.  A few places were accidentally
making copies of the list before iterating over them (value assignment).
Created an enum for DEAD, LIVE, etc.
Fix an assert in non-debug builds

This assert assumes that it will only be enabled if
isTransDBEnabled == true.
Allow traits to be created in extensions

It seems like it should exist for completness.
I needed this for adding a trait to the fb extension but I'm
breaking it out because I'm going a different direction with
that diff but it seems generally useful.
Remove unused ArgDesc::genCode
Move/delete various files from hphp/bin, change tools to a link
Optimized way to call $cont->{next,send,raise}()

Caching pointers to HPHP::VM::Func improved overall CPU time by about
2%, simplifying invokefunc() by another 1.5%.

Once asynchronous functions are natively implemented, we will be able to
eliminate >95% of these VM reenters.
Remove disabled SpillStack optimization

I think this isn't necessary now because we use GuardStk and
AssertStk to get type information into the stack.  Unless I'm missing
something, I think we shouldn't be generating any cases where we spill
something back to right where we loaded it from anymore.  (If it turns
out we are, we implement this then.)
Expose response headers in http:// wrapper meta data