Move APPLY_TAINT_PROPER macro for general use.

The pp functions being removed from Perl_apply will need it.
Extract Perl_taint_if_args_are_tainted() from Perl_apply().

This is the last of the non-trivial code shared by all the ops in Perl_apply().

The name is a best guess at what this function does.
Extract pp_kill from Perl_apply().
Extract Perl_pp_chmod from Perl_apply.
Extract Perl_pp_unlink from Perl_apply
Extrat Perl_pp_utime from Perl_apply.
Extract Perl_pp_chown from Perl_apply.

And that is the end of Perl_apply!
Merge pull request #12 from evalEmpire/refactor/destroy_Perl_apply

Turn unlink, chmod, chown, utime and kill into their own ops.

Eliminates Perl_apply().  Makes it much easier to add autodie to these functions.

* The VMS parts may not have been extracted properly. There may be some left over break statements from when the code was in a case statement.
* Perl_taint_if_args_are_tainted() is just my best guess at what the function does.
* There's likely plenty of opportunities now to clean up each extracted op.