Add information about the TPIE_PARALLEL_SORT compile flag to sysinfo.h.
Update pipelining documentation.

The usage and call order of prepare/begin/end has changed, and the
parallel framework uses a different default thread count and has
switched to an enum for the maintainOrder parameter.
graph.cpp: Fix is_depending reporting incorrectly for evacuation.
parallel.h: Add worker index to exception message.
Set default parallel buffer size to 2048 (#68).
It is permitted to call push and step in end.
Add ut-pipelining parallel_push_in_end test.
In ut-pipelining parallel_push_in_end, test that the number of received pushes is correct.
Change parallel actor graph to be purely push-based. (#70)
In consumer::begin, wait for all threads to initialize.
Remove state_base::done and introduce new worker state DONE.
Handle pushing in end() in parallel.
Add missing ut-pipelining tests to CMakeLists.txt.
Merge branch 'issue_70'. Fixes #70.
Move parallel.h to parallel/base.h. (1/2)

Split into two commits to preserve blame information.
Move parallel.h to parallel/base.h. (2/2)

Split into two commits to preserve blame information.
parallel: Split pipes.h off from base.h.
parallel: Split factory.h off from base.h.
parallel: Split options.h off from base.h.
parallel: Split worker_state.h off from base.h.