BUG: warn that bounded method in minimize_scalar does no support relative tolerance

Only issue the warning if the tol parameter is given.
TST: sparse: catch right error type

Numpy had a bug that caused a wrong error come up here; catch the right
one.
BUG: sparse: fix dtype casting in dok_matrix __add__ and __truediv__
corrected dB in amplitude response
BLD: except clause for Sphinx import in setup.py should catch everything.

Closes gh-2926.  The Sphinx version currently shipping with MacPorts for Python
3.2 seems broken, so while a bare except is not great style it's necessary.
Merge pull request #2927 from rgommers/broken-sphinx-issue

BLD: except clause for Sphinx import in setup.py should catch everything.
Merge pull request #2917 from dlax/minimize_scalar-tol

BUG: optimize: warn that bounded method in minimize_scalar does no support relative tolerance
BUG: io/wavfile: safer writing directly from buffer

Fixes gh-2928
Merge pull request #2933 from pv/wavfile-buf

BUG: io/wavfile: safer writing directly from buffer
Merge pull request #2916 from pv/ufunc-fix

BUG: sparse: minor bugfixes
Merge pull request #2920 from ClemensFMN/db_correction

DOC: signal: corrected dB in amplitude response examples