- also a new version of utlist.h with APPEND_ELEM macro

- Demonstrated in test program.  This function allows caller to suspend
  until some other entity calls margo_finalize(). If called by a ULT
  that is executing in the same pool as the HG progress thread, then it
  will indicate to the progress thread that it does not need to yield
  execution.
- fixes #6

- fixes #1

get_size() is the right function, just keep in mind that it doesn't
count the caller, only work units that are queued for future execution
in the pool

- fixes #5
- suggested by John
- run example server as "./server single" intead of "./server" to
  demonstrate

- fixes #2