Adds runtime support for non-class typehints. Typedefs are
introduced using type statements, and autoloaded via a new autoload
map entry. Shapes are parsed but the structure is currently thrown
away and treated as arrays at runtime. This extends the NamedEntity
structure to sometimes cache 'NameDefs', which are either Typedef*'s
or Class*'s. VerifyParamType now has to check for typedefs if an
object fails a class check, or when checking non-Object types against
a non-primitive type name that isn't a class.
This change is mostly for FB internal organizational reasons.
Building is not effected beyond the fact that the target now
lands in hphp/hhvm/hhvm rather than src/hhvm/hhvm.
Jordan DeLong