ENH sparse: Add Ellipsis indexing to sparse matrices.
TST sparse: Add tests Ellipsis indexing with sparse matrices.
TST: add the Burkardt test matrices for the matrix exponential
MAINT: math.expm1 -> np.expm1 hoping for compatibility with old python/numpy
TST: clean up Burkardt expm matrix tests
TST: remove redundant code
TST: test eigenvalues instead of asserting them in comments
Merge pull request #2830 from argriffing/test-expm-burkardt

TST: add the Burkardt test matrices for the matrix exponential
ENH: sparse: simpler way to expand the Ellipsis
Merge pull request #2759 from cowlicks/sparse-ellipsis-slicing

ENH: sparse: support Ellipsis in slicing

This add indexing with Ellipsis (...) to sparse matrices.

Fixes gh-2721
BUG: special: generalized laguerre polynomial is not defined for alpha <= -1
BUG: spatial/qhull: recompute facet centers always

Qhull may fail to update them in the incremental mode.
DOC: Fix typo in signal.welch example

The example did not run since `1024` is not a valid window name.  Since
it didn't run, no figures were displayed in the online docs.

Also added calls to plt.ylim so the figures look reasonable in the docs.
S
Merge pull request #2856 from ewmoore/welch-example

DOC: Fix typo in signal.welch example
TST: spatial/qhull: refactor incremental mode test + add test for f5bd5ffc
BUG: spatial/qhull: fix a deadlock condition

Python garbage collector can run a __del__ method in principle at any
time.  If this happens inside a _Qhull method that holds the qhull lock,
and the destructor calls _Qhull.close, a deadlock ensues.

This commit makes _Qhull.close safe to run in a destructor, by
postponing the cleanup if the lock is held.

This issue affects only code using the incremental=True mode, as in
other cases the cleanup is performed immediately after use and not from
the destructor.

Also, remove the __del__ method from _Qhull so that the close() method
is never called from the class's own destructor.
TST: spatial/qhull: re-enable a pathological test case that now works
Merge pull request #2858 from pv/voronoi-inc-fail

BUG: spatial/qhull: fix bug in incremental Voronoi + a deadlock
Merge pull request #2855 from pv/genlaguerre-restrict

BUG: special: generalized laguerre polynomial is not defined for alpha <= -1
Fixing unicode support for method name in cluster.hierarchy.linkage (Trac 1887)