Thread safety: step 1: cleanup

[DennisHeimbigner]

re: #1373 (partial)

• Mark some global constants be const to indicate and to make them easier to track.
• Hide direct access to the ncrc_globalstate behind a function call.
• Convert dispatch tables to constants (except the user defined ones)
  This has some consequences in terms of function arguments needing to be marked
  as const also.
• Remove some no longer needed global fields
• Aggregate all the nclog related globals in nclog.c
• Uniformly replace nc_sizevector{0,1} with NC_coord_{zero,one}
• Uniformly replace nc_ptrdffvector1 with NC_stride_one
• Remove some obsolete code

[WardF]

Looks good, resolving conflicts and merging when tests end. Slowly working through the list here and over on fortran.