Added typedefs for __int64_t and __uint64_t.  These will be used to avoid explicit use of `[unsigned] long long' and `[u]quad_t'.
Added typedefs for __int64_t and __uint64_t.  These will be used to avoid
explicit use of `[unsigned] long long' and `[u]quad_t'.

Fixed disorder of and lack of comments for the types added in the previous
two commits.  Improved some comments.  The comments should be elswhere
(not duplicated in every MD file).

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase