Support for CountedCompleters waiting on a pending RPC
Add a core-load-tester
cleanup
Remove dead import
Use CountedCompleters for DRemoteTask and RPC calls.

This frees a F/J thread from blocking waiting for a top-level DRemoteTask to
complete... essentially requiring Continuation Passing Style in DRemoteTask
RPC.  RPC now supports multiple F/J tasks which a single RPC will complete
*all* of these tasks (e.g., in case many tasks are awaiting the result of
a single shared TaskGetKey).

Replace compute2 with lcompute ("local compute").  There is also a dcompute
("distributed compute"), strictly being used by DRemoteTask.
Replace fork with dfork.
Replace most invoke's with dinvoke's.  Remove many useless dinvoke's, which
now do the default dinvoke action of calling compute2().
dinvoke() requires a call to tryComplete().
Cleanup calls to DRemoteTask.init() with "@Override".
Handle canceling large GLM jobs before even the first one is made.
Lower default log level much lower.  We can (and should) raise it for
customer branches... but its painfully loud for internal dev right now.