uidna_openUTS46 overwrites its error code argument only if
there is actually an error. Hence, if the variable is not initialized to
zero it may seem to the calling code that an error has ocurred. This
diff initializes the variable and re-enables the failing test.
The Zend versions of idn_to_ascii, idn_to_unicode and idn_to_utf8 take parameters whose valid values are defined by predefined constants and whose error codes correspond to
predefined constants. This change adds those predefined constants to hiphop. It also ports two of the applicable unit tests from the Zend code base to hiphop.