Update recorder workload generator to obtain workload operation
parameters from new Recorder I/O traces (courteousy of Babak
Behzad). I/O offsets are now tracked explicitly in the recorder
traces, and workload file_id's are set to original execution file
descriptors.

The plugin was not destroying a hash table properly, causing
segfaults. Also, the workload did not close open files or
directories, causing an error on the number of open file
descriptors.

Add code sent to me from Babak @ UIUC for generating events from
their I/O trace recorder.