Change proposal for bsd.port.mk

[Marc Espie <Marc.Espie@liafa.jussieu.fr>]

There are quite a few variables in bsd.port.mk which are currently
simply defined/not defined...

Furthermore the situation is asymetric: there are also variables which have
a default value, and are always defined.

This is somewhat ackward and very inconsistent.

I would like to let stuff be more systematic, e.g., instead of 
.if defined(USE_GMAKE)

we would have:
USE_FOO?=No
.if ${USE_FOO:L} == "yes"


The replacement is systematic. This should affect few individual ports
Makefile (apart from NO_SHARED_LIBS), since we traditionally already set
USE_FOO to Yes.

There is the specific case of the NO_* variables, which might tend
to be set to the reason why this is not possible, so those would rather 
use 
.if ${NO_FOO:L} != "no"

for the current case.


There is also a case to make for systematically using
USE_FOO?=No
.if ${USE_FOO:L} != "no"
in every case.

I'd like to get some opinions before I embark on writing a tedious patch...
-- 
	Marc Espie		
|anime, sf, juggling, unicycle, acrobatics, comics...
|AmigaOS, OpenBSD, C++, perl, Icon, PostScript...
| `real programmers don't die, they just get out of beta'