ENH: add the limit shape c=0 to genpareto distribution

For c=0, genpareto is equivalent to the exponential
distribution.
BUG: use special.log1p instead of np.log1p

np.log1p(np.inf) is reported to produce nans on some platforms,
see numpy issue gh-4225
BUG: use scipy.special.expm1 instead of np.expm1
ENH: vectorize genpareto._munp

implementation is by @pbrod
BUG: special-case genpareto(c=-1)
ENH/BUG: support negative m in elliptic integrals

Prior, ellipkinc, and ellipeinc silently returned garbage for
negative m.  Both functions are still inaccurate due at extremely
large phi.
BUG: ellipkinc(p, 1) imprecise.

The old expression was imprecise for small phi and for phi very
close to pi/2.
TST: special: enable some mpmath test for incomplete elliptic integrals E and K
TST: enable ellipkinc tests against boost data
TST: Add tables driven tests of ellip(k,e)inc values with neg m
ENH: fix failing argument reduction for large phi. (ellip(e,k)inc)

The floating point multiples of pi/2 won't fit into an int.
Argument reduce into a double instead.
ENH: Improve precision of ellipeinc for small p, m in [0,1].
DOC: Improve docstrings for elliptic integrals.
BUG: sparse.linalg: make *Inv objects in arpack garbage-collectable by refcount

Setting self._method = self._method by passing self._method to
LinearOperator causes a reference cycle in the various inverse
operators. self._method = Class._method works.

The reference cycle prevents these objects from being GC'd immediately
by refcount.  Since these objects hold large amounts of data, it's easy
to run out of memory before cyclic GC runs, if eigs/eigsh is called in a
tight loop, so it's best to not create refcycles here.
TST: sparse.linalg: fix import in tests
BUG: full C code coverage of elli(e,k)inc tests.

Also address review comments.
Merge pull request #3767 from ewmoore/ellip_neg

BUG: special: support negative m in elliptic integrals
MAINT: Removed some unused code from ODEPACK

This will reduce the burden of eliminating compiler warnings and
replacing LINPACK calls with LAPACK
MAINT: integrate: Replace DGBFA and DGEFA with DGBTRF and DGETRF
MAINT: integrate: Replace DGESL with DGETRS