CRUNCH-380 Improvements based on Coverity scan

* Avoid corner case in negating Comparator return value of Integer.MIN_VALUE
* Remove dead stores
* Avoid unnecessary Math.abs on hashCode() values; it does not always return
  nonnegative values and is caught by the masking anyway
* Miscellaneous small inspection changes

Signed-off-by: Gabriel Reid <greid@apache.org>
CRUNCH-381 Use descriptions in parallelDo calls

Add simple descriptions to PCollection#parallelDo calls in library
methods so that it's easier to trace through job plans.