extensions are not used. They are necessary for the boundaryId()
function
- Updated the documentation in the .cc files
- Added some comments for the above flags in optim.opts and debug.opts.
- el2p: Removed the *.input file argument for make dist command in Makefile.am
  for el2p, as this test does not have any input file.
Reviewed by Christoph and Bernd.


git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@11655 2fb0f335-1f38-0410-981e-8018bf24f1b0