Fix hphpd crash when printing systemlib classes

Summary: fixes facebook/hhvm#4075

Reviewed By: @paulbiss

Differential Revision: D1642223
Deep initialization for constant properties

Summary: Defined constants may be ref-counted (e.g. resources) and require deep
initialization when used to initialize instance properties.

Fixes #4111

Reviewed By: @fredemmott

Differential Revision: D1658088

Signature: t1:1658088:1415137574:011205e3e604bb711437149f2ef1ed3b3be830b5
Improve fix for issue #4111

Summary: Closes https://github.com/facebook/hhvm/pull/4180

Reviewed By: @JoelMarcey

Differential Revision: D1669151

Signature: t1:1669151:1415548684:b89950d6e0f02fa8a4fc4bc0a9b17d4fb5835a07
Fixed xpath's php:functionString

Summary: Added CallerFrame before dom_xpath_ext_function_php's call to xmlXPathEvalExpression in case libxml2 needs to call back into HHVM.
The xpath query might contain ```php:functionString``` which triggers a call to any arbitrary php function.

Also fixed a bug where the arguments in an xpath php:functionString were reversed. For example, if the xpath was ```/foo[php:functionString('preg_match', '{$regex}',@​bar)]```, preg_match was being called as ```preg_match($bar, $regex)``` instead of ```preg_match($regex, $bar)```.

Closes https://github.com/facebook/hhvm/pull/4120

Reviewed By: @sgolemon

Differential Revision: D1656106

Signature: t1:1656106:1415132682:3423279074575c41ba3f39136ab2abd3f29ae232
Fix closure var_export

Summary: Just export the name of the class to avoid infinite recursion.

Fixes #4176

Reviewed By: @fredemmott

Differential Revision: D1668260

Signature: t1:1668260:1415405711:bc1f17b7b39fc980cdff4ae8a4637fcdee085784