testPq: Add 'Test N: ' to text before each test
testPq: ignore lines mentioining 'Line' in GAP output
testPq: ignore shell escape codes printed by some GAP versions
pq: cleanup insoluble_stab_gens() code; invoke GAP with '-A'
testPq: improve printing of message if GAP test failed
Makefile: add build rule for tst/GAP, to make testPq happy
Makefile: more cleanup

Remove obsolete src_dist target, and remove config.status
upon 'make distclean'.