Fix unused result warning on GCC 4.3 about distcc HOT 2 CLOSED

Generally, functions marked as warn_unused_result are marked that way because 
it is *never* correct to ignore the return value.  Looking at the supplied 
patch, the changes in src/stats.c and src/trace.c suppress the warning without 
adding any code to handle an error return.  Rather than unconditionally hide 
the warnings, it would be better to leave any warnings that you do not fix at 
this time, so that someone can easily find them later to address them by adding 
real error handling.

Modern distcc includes a configure option --disable-Werror that can be used to 
make warnings non-fatal if your goal is simply to build a working distcc.

As of SVN r763, gcc 4.6.1 builds the full distcc suite with no warnings (it 
builds successfully with -Werror).