Better tsort checker: parses cycle output, and checks that it's correct
with respect to the input.

Additional testcase, based on libcurses, that failed in the past.

Activate t5, t6. Check cycles output everywhere.

I forgot about this change: let the perl tsort-checker run faster
by not slurping the whole file in one go.

Add test that tsort fails (incorrect detection of cycle).
Based on a test case found by Dragos Ruiu (dr@kyx.net)

branches: 1.1.1;
Initial revision