- scheduler: fix egregious bug where wu_is_infeasible_fast() result
is ignored, and we send jobs to hosts that can't handle them.
- scheduler: don't check for disk space in work_needed();
do it in check_disk(), which generates a message to user.
- scheduler: add -debug_log flag, which sends stderr to
"debug_log" rather than scheduler_log.txt (for debugging)
svn path=/trunk/boinc/; revision=16578