Rename test suite files...

Rename test suite files...

...to match any of the three types:
exam*   test result for specific input (like a pupil's exam)
check*  test coherence of results among each other, for random input
time*   measure run-time

All tests are still there, but maybe elsewhere:
* rename match_bug.cpp => exam_match.cpp
* rename heur_gcd_bug.cpp => exam_heur_gcd.cpp
* rename bugme_chinrem_gcd.cpp => exam_chinrem_gcd.cpp
* rename parser_bugs.cpp => exam_parser.cpp
* rename exam_cra.cpp => check_cra.cpp
* include numeric_archive.cpp => exam_archive.cpp
* include pgcd_infinite_loop.cpp => exam_pgcd.cpp
* include pgcd_relatively_prime_bug.cpp => exam_pgcd.cpp

These two have been deleted, since memory leaks are best looked for
using tools on real programs on a regular basis (they were also not
automatically executed):
* delete parser_memleak.cpp
* delete mul_eval_memleak.cpp