MAINT: add pyflakes to Travis
MAINT: initialize variables to make pyflakes happy

The variables will receive their values during the running of the value.
BUG: fix missing imports etc typos found by pyflakes
BUG: io/arff: remove dead code

The `types` and `r_mend` variables are undefined, making the routines
tokenize_multilines and floupi inoperable.
BUG: sparse/bicgstab: remove call to undefined routine

There's no routine get_psolve. Just assume psolve is given.
MAINT: weave: dead code removal in benchmark
MAINT: clean up list comprehension redefining variables

Not bugs per se here, but let's make pyflakes happier.
Merge pull request #3384 from pv/travis-pyflakes

MAINT: add pyflakes to Travis-CI