Fix potential variable naming collision. (#97)
Fix potential variable naming collision. (#97)

original_zend_execute_internal and original_zend_execute_ex were
previously visible outside the extension (which could create conflicts).

These are now namespaced and static as they are meant to be internal
implementation details.
census-instrumentation/opencensus-php,census-instrumentation/opencensus-php,census-instrumentation/opencensus-php,census-instrumentation/opencensus-php,census-instrumentation/opencensus-php