Re-tooled mandocdb using sqlite3 and ohash.

Re-tooled mandocdb using sqlite3 and ohash.
See the tech@ mailing list entries in June 2012 for details, as well as the
discuss@ mailing list entries from March 2012.
Among other changes, this utility now:
 1.  uses a single sqlite3 database instead of several berkeley dbs
 2.  stores utf-8 encoded strings
 3.  using ohash to aggressively hash its contents
 4.  using fts() instead of manually walking directories