added dbConfig and dbPrepared classes
  moved query related functions to dbPrepared class
database connection pools are now also pooled
  databases are automatically shared between plugins if their configs match
added hasFailed() function
renamed getLock() function to getConnLock()
deleted dbPool_MySQL class - not needed

git-svn-id: http://pxncommon.googlecode.com/svn/trunk@23 f5fbd6b6-c213-558c-f92f-5ab434f62466