Old: scheduling has 2 phases:
1) computing a list of jobs to run (a vector of RESULT*);
this is done infrequently
2) enforcing the schedule; this is done more frequently
Problem:
when we enforce the schedule,
the RESULTs in the jobs-to-run list may not still be runnable,
and in fact they may not still exist (dangling pointer).
New: combine the 2 phases
svn path=/trunk/boinc/; revision=22792