Fix print_cache
Test to check bug in dsolve
Explicitly define variables in the polys benchmark

This avoids an enormous number of pyflakes errors for this file.
Explicitly define variables in bench_groebnertools.py
Fix _extract_facts: don't fail if expr is bool
Merge pull request #2389 from asmeurer/polysbench

Explicitly define variables in the polys benchmark
Fix issue 3633: raise if assumptions are not satisfable
Added @XFAIL test
Merge pull request #2379 from Manoj-Kumar-S/constant

Added XFAIL test for dsolve
Merge pull request #2394 from skirpichev/3633-inconsistent-assumptions

Fix issue 3633: inconsistent assumptions
Merge pull request #2375 from flacjacket/iteritems_fix

Fix print_cache