the testsuite to count them as errors of the same kind

three additional files once that we have already open()ed the
big bunch of file descriptors.

SAFETY_MARGIN additional files once that we have already open()ed
the big bunch of file descriptors.

open file limit.  In this case the test is skipped with a
message showing this limitation when the number of open files
needed for the test is greater than 256.

and avoid using ! as last char of line.

disabled for now.

are sorted out.

Try to avoid this problem checking for some possible unsupported options,
and avoid using them in the configuration file.

in the PATH and afterwards in other common locations.

and added tests 290 and 291 to check.