ENH: optimize: curve_fit now warns if pcov is undetermined

Marked the test as a knownfailure for now. The test fails because
assert_warns in numpy.testing should clean __warningregistry__...
FIX: re-enable test for indertemitate covariance warning

Fixed the bogus waring in test_array_like and thus now we can
re-enable the test for the issuing of OptimizeWarning from curve_fit
when the covariance matrix is indeterminate. This works as long as in
the future new tests don't trigger the warning somewhere else in scipy
test suite ;)
MAINT: stats: Add note about change to scoreatpercentile in release 0.12.0.

Also make a test of scoreatpercentile on a 2D array more explicit
about the expected result.

Closes gh-3329.
DOC: sparse.linalg: typo
ENH: sparse.linalg: take LinearOperator in svds

Should allow solving PCA for sparse matrix.
DOC: advertise svds(LinearOperator) + vanity
BUG: Match exception declarations between scipy/io/matlab/streams.pyx and
scipy/io/matlab/streams.pxd to prevent an error in recent versions of
cython.
Fix PEP8 W391 issues (blank line at end of file).
Fix PEP8 E712 issues (comparisons to True).
Misc PEP8 fixes.
BUG: fitpack: avoid a memory error in splev(x, tck, der=k)

for x < t[0], splev(..., der=k) produces garbage or crashes
because of a memory error.

Fixes gh-2188
Deprecate nanmean, nanstd, nanmedian in favour of the numpy equivalents

See #1727
TST: stats: filter out DeprecationWarnings in TestNanFunc
Latest changes from standalone idlsave:

- Properly handle null data
- Added support for description records
PEP8: fix line too long
ENH: mention OptimizeWarning in curve_fit docstring
BUG: Raise exceptions when an invalid file position is returned.
BUG: fix ndimage functions for large data

map_coordinates uses int to index into data arrays which can overflow
for arrays of several gigabytes size. Patch by @cgohlke.
some other occurances of int replaced by npy_intp for safety.
Closes gh-3733
Fix documentation error for nc chi-squared dist

Fix documentation error for the PDF of the non-central chi-squared continuous
distribution, which was described wrong but implemented correctly. Also do some
minor style fixes (remove spaces at line end).
Merge remote-tracking branch 'upstream/master' into chi2-documentation-fix