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)

Author: laanwj

src/init.cpp

@@ -603,6 +603,9 @@ bool AppInit2(boost::thread_group& threadGroup)
     LogPrintf("\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n");
     LogPrintf("Bitcoin version %s (%s)\n", FormatFullVersion(), CLIENT_DATE);
     LogPrintf("Using OpenSSL version %s\n", SSLeay_version(SSLEAY_VERSION));
+#ifdef ENABLE_WALLET
+    LogPrintf("Using BerkeleyDB version %s\n", DbEnv::version(0, 0, 0));
+#endif
     if (!fLogTimestamps)
         LogPrintf("Startup time: %s\n", DateTimeStrFormat("%Y-%m-%d %H:%M:%S", GetTime()));
     LogPrintf("Default data directory %s\n", GetDefaultDataDir().string());