Convert string|array union parameter types

[kocsismate]

Convert strtr() and mail().

[nikic]

Windows build failure looks legit.

[nikic]

Not sure, but the Windows test failure might be because the null argument is now accepted (in line with general zpp rules), while previously the second mail call would fail at that point?

It's really hard to say because https://github.com/php/php-src/blob/master/ext/pcre/tests/bug72463_2.phpt uses EXPECTREGEX and I'm not sure what the usual output is and what we get now.

@cmb69 Could you take a look at what's going on here?

[kocsismate]

I also suspected the null argument to be the issue, but wasn't sure and also couldn't try. :/ So, Christoph's help is welcome :)

[cmb69]

Well, indeed, the failing tests hadbeen caused by an unrelated bug which has been fixed in the meantime, and after the rebase everything looks good. I think this is good to be merged. Thanks.