Use absolute import so we don't accidentally import the old pyparsing from matplotlib 1.1.1 (or earlier) if it's still around in the user's site-packages.
Use gswin64c, if found.
Merge pull request #2266 from mdboom/fix-pyparsing-cruft

pyparsing version parsing error
Merge pull request #2278 from mdboom/gs-win64c

Can't find 64-bit GhostScript on win64
Merge branch 'v1.3.x'