Fixed: database migration error (NULL default on NOT NULL column
'stack')
Better RNG for crypto key generation.

New code gives the user a choice from /dev/urandom, /dev/random, rand(),
and Mersenne Twister (mt_rand).
Auto-detect RNG

If no RNG is configured, or the RNG is configured as "auto", we'll try
the 'safe' options one by one until one works.

We won't try /dev/random, even though it provides the best possible
entropy, because it will block on most systems if available.
Merge branch 'master' of github.com:bolt/bolt
Merge pull request #613 from tdammers/master

Fixed: database migration error (NULL default on NOT NULL column