MySQL connection wrapper improvements:    - Follow-up to r4341, ping before rollback   - Try to not close an already closed connection, should fix #4802
MySQL connection wrapper improvements: 
  - Follow-up to r4341, ping before rollback
  - Try to not close an already closed connection, should fix #4802

git-svn-id: f68c6b3b1dcd5d00a2560c384475aaef3bc99487@4962 af82e41b-90c4-0310-8c96-b1721e28e2e2

dafrito/trac-mirror,dafrito/trac-mirror,dafrito/trac-mirror,exocad/exotrac,exocad/exotrac,moreati/trac-gitsvn,exocad/exotrac,moreati/trac-gitsvn,dokipen/trac,dokipen/trac,moreati/trac-gitsvn,dafrito/trac-mirror,exocad/exotrac,dokipen/trac,moreati/trac-gitsvn