Making Pylint faster 3 (2)

[nickdrozd]

(Something got messed up while pushing changes and #545 got closed. This is essentially the same PR.)

Here are times from using the lru_cache. A lot of stuff has been added to pylint since I last measured, so these times are higher than the previous ones.

master

real	4m32.310s
user	3m51.296s
sys	0m13.453s

real	4m28.269s
user	3m47.220s
sys	0m13.167s

real	4m30.490s
user	3m48.246s
sys	0m13.341s

cache lookup

real	3m59.156s
user	3m17.773s
sys	0m13.364s

real	3m58.147s
user	3m17.060s
sys	0m13.311s

real	3m57.503s
user	3m15.869s
sys	0m13.449s

[PCManticore]

Thank you @nickdrozd