Fix for phar:// stream wrapper with no stub

Summary: `__HALT_COMPILER()` is not required for *.phar files that are used with `phar://` stream wrapper, while HHVM throw exception `__HALT_COMPILER(); must be declared in a phar`.
As workaround I've added private variable to prevent check for `__HALT_COMPILER()` when calling from stream wrapper's method `getPharAndFile`.
In addition `\n` removed from halt token check, because it can be written even on the same line with previous code and even without any spaces before, which is allowed, for instance, such stub:
```php
<?php
echo 'something';__HALT_COMPILER();
```

This is fix for https://github.com/facebook/hhvm/issues/4012
Closes https://github.com/facebook/hhvm/pull/4080

Reviewed By: @ptarjan

Differential Revision: D1643091

Signature: t1:1643091:1414566279:a174fa099ea21459759e61c3c9884ee2ba6bfc24