Add Python 3.4 to .travis.yml

I don't know if Travis actually supports it yet. I guess we'll find out.

For the slow tests, we only tested on the most recent version of Python 2 and
Python 3, so change them from 3.3 to 3.4.

This is a lot of Pythons now. We should probably think about dropping 3.2
support...
Makes IndexedBase consistent with Symbol wrt to latex printing
Adds test extra test for latex of IndexedBase
Added files and docs for primary field functionality
Merge branch 'master' of https://github.com/sympy/sympy into fielddocs
Added documentation for fieldfunctions, rectified errors
Made changes suggested by @smichr
Merge branch 'master' of https://github.com/sympy/sympy into fielddocs
Fix conjugates of associated Laguerre polynomials
Add conjugation for 'assoc_legendre' polynomials
More tests on conjugation of polynomials
One more conjugation test
Merge pull request #7454 from raoulb/fix_conj_assoc_laguerre

Fix conjugates of associated Laguerre polynomials
Merge pull request #7354 from bjodah/fix_latex_IndexedBase_gamma

Makes IndexedBase consistent with Symbol wrt to latex printing
Merge pull request #7301 from asmeurer/python3.4

Add Python 3.4 to .travis.yml
Rename subset() to is_subset() and add is_superset() #7460

The subset() method is now marked as deprecated. The is_subset() method
also has a different semantic meaning now.

Earlier, self.subset(other) checked if 'other' is a subset of
'self'. However, now with the renaming it makes more sense that the
method call self.is_subset(other) is interpreted as check if 'self' is a
subset of 'other'.

A corresponding is_superset() method has been added to allow checking if
one set is a superset of another.
Merge pull request #7346 from amitsaha/is_subset

Rename subset() to is_subset() #7460
Merge pull request #7407 from srjoglekar246/fielddocs

Docs for field functionality added to physics.vector