HHVM support

[thekid]

Fatal error: f_get_extension_funcs is not supported: extensions are built differently in /devel/xp/compiler/src/main/php/xp/compiler/emit/php/NativeImporter.class.php on line 92

[thekid]

After applying a fix to no longer use get_extension_funcs() which produces the above error, tests are failing due to:

[0500] Exception lang.IllegalArgumentException
(Function vsprintf is not inside extension standard (but (n/a)))

According to some research I conducted, there's nothing we can do except not verifying the extension.

[thekid]

Also fixed incompatibilities w/ sscanf() - now tests are passing on HHVM!