.warning directives in Makefile

[Sergey Matveychuk]

Hi.

It was a long time ago and I don't remember if was a discussion about 
.warning directive. As I can see only .error directive was documented in 
Porters' Handbook as a harmful.

But I'd like remind .warning directive pollutes stderr and discouraged 
portupgrade which was designed to catch messages from stderr and rises 
errors.

Now there are a few ports (ImageMagic and GhostScript*) where the 
directive was appeared. I think the ports should be fixed to use 
ECHO_MSG to display the warnings.

Thanks.
-- 
Dixi.
Sem.