Tag aliases do not work?

## Description
Tag aliases seem to unconditionally throw an exception when trying to run a test with a tag alias.

### Steps to reproduce
Put ```CATCH_REGISTER_TAG_ALIAS("[@myalias]", "[myalias]")``` somewhere
You can use debugger to see that it is indeed executed.

Then put ```["@myalias"]``` on a tag somewhere in scenario.

Try to run the test. It crashes with:

> terminating with uncaught exception of type std::domain_error: Tag name: [@myalias] is not allowed.
> Tag names starting with non alpha-numeric characters are reserved
> \__FILE__:\__LINE__
Aborted

### Extra information
I'm not sure how this would ever work because in catch.hpp ```enforceNotReservedTag``` and ```makeTestCase``` does not check if the ```tag``` is a registered alias or not?

Thus it seems it would always fail?