* Casting from 'type **' to 'const type **' is not allowed by C.

* Since write, mmap and a number of other functions are not part of
  ISO C (i.e. strictly conforming programs must not use those), we need
  to ensure the build environment provides POSIX conformance.
* This mostly prevents unrelated bug reports later on.
* From POSIX 2008, CDI unconditionally only uses getline and has a
  work-around in case that is missing.

* This way re-ordering of GRIB records does not change checksums.

This reverts commit b5845133.

* The previous elimination of components created a subtle data corruption bug.

* This was introduced erroneously in "Renamed DATATYPE_ to CDI_DATATYPE_."
  aka c05b576e.

* Also fixes trailing whitespace in Fortran interface.