Compilation warnings

As of r9396, the trunk software has had all warnings eliminated when
using GCC 4.2.3 on Ubuntu 8.04.

A new configure option:

./configure --enable-warnings-as-errors

…will let you test the compile in your configuration. This is
turned off by default (as has always been the case.)

Note, this only applies to the host code; there are still some
warnings in the USRP FX2 firmware that will display (but not error

We encourage testers to try this out when compiling the trunk code and
let us know here or by creating bug reports in Trac.

Johnathan C.
Corgan Enterprises LLC