Properly finalize prepared SQLite3 statements to prevent memory leak

The AstDB uses prepared SQLite3 statements to retrieve data from the SQLite3
database.  These statements should be finalized during Asterisk shutdown so
that the SQLite3 database can be properly closed.  Failure to finalize the
statements results in a memory leak and a failure when closing the database.

This patch fixes those issues by ensuring that all prepared statements are
properly finalized at shutdown.

(closes issue ASTERISK-20647)
Reported by: Corey Farrell
patches:
  astdb-sqlite3_close.patch uploaded by Corey Farrell (license 5909)
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Merged revisions 375761 from http://svn.asterisk.org/svn/asterisk/branches/10
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Merged revisions 375763 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@375770 65c4cc65-6c06-0410-ace0-fbb531ad65f3