* Do not create unnecessary temporaries.

* The previous implementation was not thread safe (accidental SAVE
  attribute) and handled string arguments of full length without a
  c_null_char terminator incorrectly.

* Correct return value when grib_get_length is available.

* Also use canonical notation for pointer variables and
  consistently use uuid[CDI_UUID_SIZE] for UUID passing.
* Whitespace before the # of preprocessor defines is not portable.