Add a docstring
Revert "Checkout 0.7.3 before testing in Travis"

This reverts commit 3d56d4b8c1d8346bc92bc23487cbb82214c6c476.
Merge branch 'master' into matrix_hash

Conflicts:
	sympy/matrices/tests/test_matrices.py
Merge branch 'matrix_hash' of github.com:asmeurer/sympy into matrix_hash
Merge pull request #2274 from lidavidm/issue_3943

Issue 3943: document integral_steps, which Gamma uses
Typo agregator -> aggregator.
Typo python -> Python.
Typo: look this -> look at this.
Rework infinitesimals docstring.
Fix dsolve reference under Hint Functions.
Fix logcombine reference.
Rework awkward language under constantsimp.
Fix references to several ode functions.
Shorten function references under "See also" headers.
Rewrap with tw=78:et.
Fix the simplification of Order at Infinity.
Printing of Order at infinity.
Add tests for Order at Infinity.
Add printing tests for Order at Infinity.
Indentation fix.