BUG: sparse: fix operator overloading with custom types

See issue #3580.
ENH: sparse: inplace ops should fall back to x = x op y if not implemented
Merge pull request #3484 from rgommers/mingw64-qhull

BLD: fix Qhull build issue with MinGW-w64.

Closes gh-3237.
Merge pull request #3546 from tacaswell/test_hierarchy_mpl_import

TST : make tests use non-interactive matplotlib backend
BUG: lobpcg returned wrong values for small matrices (n < 10)
Merge pull request #3594 from argriffing/small-fiedler-lobpcg

BUG: sparse.linalg: fix bugs in lobpcg symeig function

eig() doesn't necessarily return sorted eigenvalues
MAINT: fix coverage and coveralls

Ensure .coveragerc is in the directory where the tests are run, and make
submission coveralls.io generate correct path names.
MAINT: remove most references to symeig and move lobpcg benchmarks out of the test directory
MAINT: remove the rest of the symeig references
DOC: move docs from __init__.py to the lobpcg docstring
Merge pull request #3342 from robfalck/linprog

ENH: linprog function for linear programming
MAINT: avoid clobbering numpy.ma as ma
MAINT: change variable name 'iter' to 'nit' -- these names are used interchangeably in the code, but 'iter' is a python built-in function
MAINT: versionadded 0.14.0 -> 0.15.0
MAINT: avoid backslash for line continuation
STY: docstrings lines over 80 characters
STY: if not x is None -> if x is not None
TST: add a network flow test
TST: numpy.testing assertions already report the actual and desired values; also use a more sophisticated warning assertion
TST: test network flow with edges that have costs and limited capacities