mno-async_writes/server: Fixed OSD crashes by:

- backporting revision 3116 from the trunk
- adding a quickfix regarding a out of bounds exception (occurred when
  the RPC Client tried to delete a request from the send queue which was
already removed by checkTimers()) 


git-svn-id: https://xtreemfs.googlecode.com/svn/branches/mno-async_writes@3129 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534