TST: run PEP8 and Pyflakes on the same TravisCI worker.

Saves a little runtime, but more importantly less chance for flaky (no pun
intented) results due to git submodule update failures etc.
Merge pull request #3456 from rgommers/travis-pep8

TST: run PEP8 and Pyflakes on the same TravisCI worker.
DOC: add more details to deconvolve docstring, link to np.polymul/polydiv.

Note that matlab uses conv for both operations.
DOC: add more precise link to R documentation in mstats.mquantiles.
TST: signal: ignore warnings generated by chebwin
MAINT: remove unused import
TST: stats: Fix some spurious warnings generated when the stats unit tests are run.

When given a negative argument, special.bdtr and special.pdtr return nan, and using
a nan value in a numpy comparison generates a warning.  This commit ensures that
the values used in the comparison that takes place in binom._ppf and poisson._ppf are
not nan.
Merge pull request #3481 from WarrenWeckesser/chebwin-test-warning

TST: signal: ignore warnings generated by chebwin
Merge pull request #3482 from WarrenWeckesser/discr-warnings

TST: stats: Fix some spurious warnings generated when the stats unit tests are run.
correct doc for epsfcn in leastsq

See fdjac2 for determination of the step length. Original docs would lead you to beleave epsfcn is the actual step length
[BUG] fix scipy.linalg.hessenberg

do not permute the input matrix. fixes #3364.
MAINT: io: Remove empty strings warning from idl.py

This warning has been in the code for quite a while (therefore people who
use it already know about it), and it can be rather annoying and verbose
when reading large arrays with empty strings because it is printed for each
occurrence. I propose to get rid of these warnings altogether.
MAINT: io: Remove multi-dimensional structures warning from idl.py

The warning has served its purpose, and is no longer necessary.

Also removed the filtering of the now nonexistent warnings from the
idl tests.
MAINT: io: remove a couple unused variables in idl.py (thanks, pyflakes)
Merge pull request #3498 from WarrenWeckesser/tiagopereira-patch-1

MAINT: io: remove old warnings from idl.py
Merge pull request #3495 from bmcage/docleastsq

correct doc for epsfcn in leastsq
[TST] linalg.hessenberg: add unit test

add the example from #3364 as unit test.
PEP8: add ignore E126 to tox.ini.  Changed from E121 in pep8 1.5

There were 910 errors for E126, which is too many to fix now.
PEP8: fix E111 and E113 (indentation unexpected / not a multiple of 4) errors.
PEP8: fix E112 ("expected indented block") errors.