bugfix Db::open/close and zombie sockets bugs fix double-close of socket handle,

keep databases open,
close db cursors,
initial block download in batches of 500 blocks,
fix misc warnings,
subver linux-test8

serialize.h

@@ -20,6 +20,7 @@ class CDataStream;
 class CAutoFile;
 
 static const int VERSION = 106;
+static const char* pszSubVer = " linux-test8";