Issue #17713: Added failure diagnostics to test.
Close #17731: Clean up properly in test_import
Merge fix for #17731 from 3.3
Issue #17728: Specify default precision for float.format for presentation types e, f, and g.
Issue #17728: Merge with 3.3.
#13510: clarify that f.readlines() is note necessary to iterate over a file.  Patch by Dan Riti.
#13510: merge with 3.3.
Issue #17710: Fix pickle raising a SystemError on bogus input.
Issue #17710: Fix pickle raising a SystemError on bogus input.