Add -x flag to help with debugging.
Reorganize headers and some defines.
Use 5 second stoptime.
Group globals.
fd == 0 is valid.
Abort benchmark on failure.
Simpler code.
Fix a hidden HDFS test failure caused by fstat resolving a path twice.
Use unbuffered writes/reads.

This is a rather big oops in this benchmark tool as buffering negates any
effect of playing with the length of the buffer.
Don't reject pwrite with offset > current length.

This was wrongly changed in the recent chirp_alloc overhaul.
Write consecutively to the file and abort the loop if there is a failure.
Correct problems in chirp_benchmark and Chirp+HDFS.

* chirp-hdfs-bugfix:
  Write consecutively to the file and abort the loop if there is a failure.
  Don't reject pwrite with offset > current length.
  Use unbuffered writes/reads.
  Fix a hidden HDFS test failure caused by fstat resolving a path twice.
  Simpler code.
  Abort benchmark on failure.
  fd == 0 is valid.
  Group globals.
  Use 5 second stoptime.
  Reorganize headers and some defines.
  Add -x flag to help with debugging.