BUG: Fix the automatic frequency selection of scipy.signal.bode.
The automatic selection of the frequencies could miss zeros or resonance peaks, so use the existing function scipy.signal.findfreqs instead of _default_response_frequencies.

Specific changes:
* Modifed the function scipy.signal.bode to use scipy.signal.freqs.
* Added a docstring to scipy.signal.findfreqs.
BUG: special: multigammaln returned wrong size array (closes ticket #1849)
add mode argument to ndimage.imread and use context manager
DOC: Add plots to examples
DOC: fix definition list typo
DOC: special: Added docstrings for gdtria, gdtrib and gdtrix.

The terse docstring style of the scipy.special ufunc docstrings
is maintained, but they include examples.
DOC: special: write proper docstring for gdtria, gdtrib, gdtrix.
DOC: special: add a description of the optional fourth argument for gdtria, gdtrib and gdtrix.
DOC: special: add the function signature to the top of the docstrings for gdtria, gdtrib and gdtrix.
Merge pull request #459 from WarrenWeckesser/special-gdtri-docstrings

DOC: special: Added docstrings for gdtria, gdtrib and gdtrix.
Merge pull request #457 from juliantaylor/imread-mode

ENH: ndimage: add mode argument to ndimage.imread
DOC: add plt.show() to examples
DOC: signal: add docstring for deconvolve()
Merge pull request #458 from endolith/patch-4

DOC: interpolate: Add plots to interpolation examples
Merge pull request #455 from WarrenWeckesser/bug-multigammaln

BUG: special: multigammaln returned wrong size array (closes ticket #1849)
Merge pull request #432 from WarrenWeckesser/bode-freqs

BUG: signal: Fix the automatic frequency selection of scipy.signal.bode
ENH: sparse: min and max methods on matrices with .data, except dia

axis keyword not supported (yet).
TST: sparse: refactor minmax test
Merge pull request #451 from larsmans/sparse-min-max

ENH: sparse: min and max methods for CSR & CSC & COO