HEADS UP: -Werror re-enabled in WARNS

Roughly 6 months ago, -Werror was disabled while gcc 4.2 was
imported and bedded in.

I've fixed a number of the compiler warnings that were causing
the build to barf. In a few cases I reduced the WARNS level
instead of making lots of changes.

I tested the changes with a 'make universe', so hopefully
tinderbox builds will continue to work. Of course if you have
work in progress that doesn't compile cleanly and a WARNS
level set, you may find your build now breaks.

--
John Birrell