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* And use that if available.

* It's at the moment identical to the 1D test. That will change with the next commit.

* This also adds separate documentation, header, Fortran wrappers and
  pkg-config file for the cdi-pio part of the library

* If these are set they already override the corresponding variable.
* Also reduce number of spurious linefeeds in configure.

* These can be used to e.g. replace CC=gcc with CC="scorep gcc" after
  running the configure tests.

* This reduces conflicts arising from later changes of PATH at build
  vs configure time.

* At least for more recent versions of distutils:sysconfig.