Merge pull request #2585 from jrioux/piecewise

Piecewise integration fix
added missing import
Sort the args of Xor.

Complement to issue 4081.
Remove sorting from printer (Equivalent/Xor args are sorted already).
Merge pull request #2579 from skirpichev/misc

Misc small fixes
Blacklist numeric-computation.rst tests if numpy or theano modules are not imported
Fix tests in numeric-computation.rst
Install numpy for numeric-computation.rst if TEST_THEANO is true
Merge pull request #2428 from gilbertgede/fix_lambdify

Fixed minor dummification issue.
merged master
Indices renamed
Merge pull request #2418 from asmeurer/isympy3

Don't install isympy as isympy3 in Python 3
Merge pull request #2060 from asmeurer/textplot

Use / or \ in textplot if the function is increasing or decreasing
more code factorisation
Merge pull request #2433 from jrioux/translation

Remove translation cruft.
Revert cbrt printing
Revert "Fix tests for cbrt"

This reverts commit c9af0d8d3c2be305e9d028418de69dfb8bcaacf2.
Merge branch 'master' into 4071-cbrt
Fix printing in doctests
Add tests