bitcoin auto-renice-ing

It sets different priorities for each thread.  The generate threads run at PRIO_MIN.  The other threads rarely take any CPU and run at normal.

#define THREAD_PRIORITY_LOWEST          PRIO_MIN
#define THREAD_PRIORITY_BELOW_NORMAL    2
#define THREAD_PRIORITY_NORMAL          0

The priorities converted from Windows priorities were probably from a table like this:

   "The following table shows the mapping between nice values and Win32 priorities. Refer to the Win32 documentation for SetThreadPriority() for more information on Win32 priority issues.

nice value    Win32 Priority
-20 to -16    THREAD_PRIORITY_HIGHEST
-15 to -6    THREAD_PRIORITY_ABOVE_NORMAL
-5 to +4    THREAD_PRIORITY_NORMAL
+5 to +14    THREAD_PRIORITY_BELOW_NORMAL
+15 to +19    THREAD_PRIORITY_LOWEST"

If you have better values, suggestions welcome.

Also, there was some advice on the web that PRIO_PROCESS is used on Linux because threads are processes.  If that's not true, maybe it accounts for unexpectedly setting the priority of the whole app.

    // threads are processes on linux, so PRIO_PROCESS affects just the one thread
    setpriority(PRIO_PROCESS, getpid(), nPriority);