mangle C++ ::std and ::std::allocator correctly

On Linux, there are shortcut mangles for ::std and ::std::allocator which were not implemented.

Not done on Windows because C++ template mangling currently isn't done at all on Windows. Need to fix that with another PR.

Also wound up removing some tabs from the test files.
And if you had code to check for those, then that would be a good argument.  But as it is the variable is useless.

Adding useless code is not clever forward thinking, it's just useless code.