BLD: fix MinGW Windows build issue by splitting linalg.interpolate sources.

Type of errors that this fixes::

    Argument #5 (named `ifac') of `zfftb1' is one type at (2) but is some
    other type at (1) [info -f g77 M GLOBALS]

Warning shows up with gfortran as::

    Warning: Type mismatch in argument 'ifac' at (1); passed REAL(8) to INTEGER(4)

Closes gh-2709.
BLD: ignore split Fortran source files created by the build process.

Also add some other generated files to .gitignore
BLD: use relative paths in linalg/setup.py
MAINT: address review comments on splitting Fortran files at build time.
BLD: exclude split Fortran files from sdist generated source bundles.
TST: silence test warnings about deprecation of expm2/expm3.
BUG: Raise error when attempting to create dtype=object sparse matrix.
DOC: Add note about SciPy being for numeric data.
ENH: Add getrow and getcol to DOK.
BUG: Fix casting in _mul_scalar for DOK and LIL.

The way I did the casting is pretty hackish. There should be a better
way.
TST: Turn on scalar multiplication tests for LIL and DOK.
BUG: Remove broken take and split methods from DOK.
ENH: sparse: move scalar upcast dtype computation to a helper function
MAINT: sparse: convert object dtype error to a warning
Merge pull request #2719 from cowlicks/dok-lil-improvements

BUG: sparse: DOK and LIL improvements

* Raise a warning when you try to create a sparse matrix with
  dtype=object, and add a note to the docs stating that SciPy Sparse is for
  numeric data.
* Remove the broken and undocumented take and split methods from DOK, add getrow and getcol.
* Fix the casting for scalar multiplication with LIL and DOK and turn on tests for them.

Fixes gh-2528, gh-2645, and gh-2542.
BLD: recognize one more Fortran comment character
Merge pull request #2761 from rgommers/fix-mingw-compilation

BLD: Fix MinGW compilation by splitting source files

Fixes gh-2709
MAINT: attempt debugging some code that behaves differently on different LAPACKs
MAINT: disable a test that involves singular matrices and which seems to not be stable across different LAPACKs
Merge pull request #2768 from argriffing/lax-fractional-matrix-power-singularity

TST: mark a fractional_matrix_power test as knownfail