Small modifications to PHP exception/error handling

[mockey]

make HExceptions with an error code != null catchable, i.e. HExceptions from _hx_error_handler
remove duplicated error message, filename and line in HException from _hx_error_handler

[mockey]

Some explainations (only if you're interested ;-):
There is this class HException, which extends the normal PHP Exception. It is needed as a wrapper so you can throw "anything" because PHP5 can only throw Exceptions. But the HException can never be caught as an Exception because of this hard coded line in genphp:
https://github.com/HaxeFoundation/haxe/blob/development/src/generators/genphp.ml#L1565
While this makes sense for things thrown from Haxe, it is not so good for HExceptions, that are thrown from _hx_error_handler, that covers error handling from PHP. So I added a check if the error code is set, which should only be set from the error handler.
Also I removed some duplicate text (message, file, line) from the HException that is thrown from _hx_error_handler.
This whole HException class should maybe be made private or something. It makes no sense to use it in Haxe code.

[Simn]

My first question is always if there's any way we can test this.

[mockey]

Exceptions can be tested in the test runner, I suppose? So when I catch an exception I can check its type and then proceed, right?

[Simn]

Yes, there should be an exc function which can be used to check exceptions. I don't know if that allows checking exception types though, so maybe just something custom would work best.

[mockey]

I'll try to make something up.

[Simn]

You'll have to change the test, it currently causes src/unit/TestIssues.hx:16: characters 30-39 : Module unit.issues.Issue4973 does not define type Issue4973 on all targets but PHP. Try #ifing out the test function instead.