Add pragma(error) and pragma(warning) to the language.

[Tobias Pankrath]

I'm currently writing some template based code and there are 
situations, when I want to issue warnings or errors to users of my code.

I know of pragma(msg), but the output will be formatted differently from the
normal compiler warnings / errors. This is bad for tool integration and the
messages will likely not catch the eye of a normal user.

Therefore I propose to add two pragmas pragma(error) and pragma(warning) to 
the core language, which work just like pragma(msg), but will format the 
message the way, the compiler would format
its own error messages or warnings.

pragma(error) should cause a real compile error, too.

What do you think?