added automatic save/resume functionality to mongo2toku #495

On exit, in addition to logging the --ts value needed for resume, we also save it to
a file __mongo2toku_saved_timestamp__ and try to read out of that file on resume.

fixes #495
increased numInitialChunks #513

The default was 2 * numShards, which was low enough that you could get a
bunch of migrations initially even when using hashed sharding.  This is
preventable by increasing the number of pre-split chunks, and there seems
to be no reason not to do this.

fixes #513
disabled logpath.js #396

die die die die die die die die die
added truncate flag for saving timestamp #495
Merge branch 'bugs/495' into bugfixes/tokumx-1.2
added NEWS for 1.2.1
Merge branch 'bugfixes/tokumx-1.2'