Adding restructure checks

To ease the process of restructuring the isisscripts I've added
a simple test that currently only checks if a file '.check' is
present in any of the subfolders. The idea is, that this file lists
all files that are accepted for the restructured setup. If any file
in a subfolder is not present, the test will fail.

Currently only the presence of '.check' is tested, not is contents.

Per default the test is skipped, to run it the BUILDCHECK variable
must be define. The simplest way to do this is to run

  'BUILDCHECK= make'

I've also changed the documentation test to only execute when BUILDCHECK
is given and fail properly. Building the isisscripts and getting a huge
list of undocumented functions did not seem to motivate anyone to fix that :)