Enable SQLite to use mmap for file access.

The time it takes to issue "SELECT * FROM tvshowview" (the first time the
TV Shows library is opened) with 345 TV shows on a non-overclocked
Raspberry Pi changed as follows. Times are in seconds:

      Before          After
      Mean   StdDev   Mean   StdDev  Confidence  Change
Time  3.352  0.132    2.550  0.021   100.0%      +31.5%

These times assume SQLite has already been upgraded to version 3080301
(see PR #4235).
Pre-populate the mmap'ed database file in SQLite.

The time taken to issue "SELECT * FROM tvshowview" in seconds improves
still further in this case.

      Before          After
      Mean   StdDev   Mean   StdDev  Confidence  Change
Time  2.550  0.021    2.375  0.043   100.0%      +7.4%

Note, this requires the standard SQLite amalgamation tarball to be patched
prior to building. The change may not be desirable further upstream due to
the fact that it might cause database access times to increase in usage
scenarios that differ from those employed by XBMC.
Merge branch 'enable_sqlite_mmap' of https://github.com/bavison/xbmc into nc3