Add -reindex, to perform in-place reindexing of block chain files

Flushes the blktree/ and coins/ databases, and reindexes the
block chain files, as if their contents was loaded via -loadblock.

Based on earlier work by Jeff Garzik.

src/test/test_bitcoin.cpp

@@ -22,7 +22,7 @@ struct TestingSetup {
         pblocktree = new CBlockTreeDB(true);
         pcoinsdbview = new CCoinsViewDB(true);
         pcoinsTip = new CCoinsViewCache(*pcoinsdbview);
-        LoadBlockIndex(true);
+        LoadBlockIndex();
         bool fFirstRun;
         pwalletMain = new CWallet("wallet.dat");
         pwalletMain->LoadWallet(fFirstRun);