fixed typo in TimeTask output introduced in commit 6c903629
Local omp.h was conflicting with system omp.h
issue #33: making grid accessors inline again
issues #23 and issue #33: using one preallocated Moments instance per thread
issue #23 and #33: accumulating Moments using multiple instances for OpenMP

  Using a grid-sized instance of Moments for every OpenMP thread
  will consume too much memory if a very large number of OpenMP
  threads are used and so is something of a stop-gap.  But the
  current serial code would be unacceptably slow in that case,
  so this shouldn't really break anything.  EMfields should be
  redesigned to contain a set of Moments instances to be passed
  from the particle solver to the field solver.
issue #33: eliminating iostream header from asserts.h