Turns out I need to use tvSet with temporaries. Also removes
unused tvSetObject*, and replaces some tvSetNull* callsites with using
make_tv temporaries.
I noticed that directorty structure of hphp/system was a bit scattered, so
I consolidated things to reduce the total number of folders and to put
related things together with each other.
This diff moves the contents of "hphp/system/classes_hhvm" into
"hphp/system", it moves the contents of "hphp/system/lib" into
"hphp/system", moves "hphp/idl" to "hphp/system/idl", and moves the
contents of "hphp/system/globals" into "hphp/system/idl".
Jordan DeLong