Merge pull request
#1951 from minrk/nbdir
minor notebook startup/notebook-dir adjustments
* change inaccurate / distressing "Overwriting profile..." log message
* `ipython notebook path` results in setting notebook-dir if it's a dir,
rather than unconditionally setting file-to-run
* file-to-run overrides no-browser
* kernels start in the notebook dir, rather than the Server's cwd
* notebook dir is validated, and created if it doesn't exist (only if parent exists, like ~all other such things)
closes
#1985
closes
#1980
