Log BerkeleyDB version at startup

Prints the actual version of BerkeleyDB that is linked against, if
wallet support is enabled.

Useful for troubleshooting.

For example:

    2014-05-01 07:44:02 Using BerkeleyDB version Berkeley DB 4.8.30: (April 9, 2010)

    2014-05-01 07:54:25 Using BerkeleyDB version Berkeley DB 5.1.29: (October 25, 20 11)
Update build instructions for Berkeley DB

- People were having problems with the .so when installing in
  alternative locations.
  Like gitian, build a static library with -fPIC that can
  be embedded into the executables.

- Add some missing steps

- Add reminder that BerkeleyDB is only needed when wallet support is
  enabled
Merge pull request #4114

bfb154e Update build instructions for Berkeley DB (Wladimir J. van der Laan)
d0a2e2e Log BerkeleyDB version at startup (Wladimir J. van der Laan)