DDPLY-AT-SCALE

The "99" limit is now gone.  Lo-priority queues default to 4*cpus.
Might be able to go down to 2*cpus.
Lo-priority F/J queues now auto-make higher lo-priority batch queues.
M/R tasks and ddply tasks now always bump batch queue depth; can be
nested 100-deep before we're in trouble (typically nesting is 2 or 3).
Unique does call nested ddply.
cbind now picks up IDs for default column names, or C1++ (e.g. instead
of "C0" or "c1")
Correct error msg for "foo==bar"
Key.isVec made public
Fix race bug in multi-chunk row-apply
Fix Frame print bug when internal Vecs are missing chunks.
Loosen Frame assert about VectorGroups; just require aligned rows.
Make far fewer new VectorGroups.
Assert new Vec keys actually are Vec keys (pass Key.isVec test)
Merge
Merge#2