[MERGE] Reduce selftest overhead to establish test names by memoization.

[Aaron Bentley]

Aaron Bentley has voted tweak.
Status is now: Conditionally approved
Comment:
I think it would be appropriate to make test_func_names an instance 
variable of TestLoader.  And according to the way other variables are 
named in this module, testFnNames should be test_fn_names.

At some point, we should investigate *why* it's being called so many 
times, but this is a good speedup IMO.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3Cm2fxxl1yzv.fsf%40free.fr%3E