BUG: add proper error handling when using interp2d on regular grids

fixes #1889
BUG: fix test for interp2d
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
TST: add the wikipedia simplex algorithm example as a test
TST: do not use zip() for bounds, because python3 can't find its len()
TST: added test from https://github.com/scipy/scipy/issues/1779
TST: rescue linear programming tests from https://github.com/scipy/scipy/pull/218
PEP8: remove spaces
TST: move some repeated code into helper functions
TST: move tests functions out of a TestCase class
STY: two blank lines between function definitions
TST: restore run_module_suite