cse hanlding of IndexedBase
Added test for cse of Indexed instances
Revert "cse hanlding of IndexedBase"

This reverts commit a574d35bd7916ba7bb30eff731984e6d6afd493e.
Added NotIterable mixin class, added same to default exclude tuple in iterable()
Added NotIterable to parents of tensor.IndexedBase (enables cse)
Tidying up of test_cse.
Added tests for iterable() on Indexed and MatrixSymbol, added xfail test of cse on matrixexpr
Extended docstring of iterable() and NotIterable
Reverted NotIterable mixin of MatrixExpr
Reverted test for iterable(MatrixExpr())
Made DeferredVector NotIterable and added test for it
Removed lint print statement in test
Add Rajath S to AUTHORS/aboutus. Welcome to SymPy!
Merge pull request #2885 from smichr/auth

Add Rajath S to AUTHORS/aboutus. Welcome to SymPy!
Merge pull request #2829 from bjodah/cse_on_indexed

Cse on indexed
Fix zero vector reexpression
Merge pull request #2887 from srjoglekar246/fixzero

Fix zero vector reexpression
travis: split slow jobs
Allow external sources for pip while installing matplotlib