matplotlib Code

Slight whitespace cleanup.

Update the axes.psd() method to reflect the new options available in mlab.psd. Add an example to show how the options change things.

Add 'pad_to' and 'sides' parameters to mlab.psd() to allow controlling of zero padding and returning of negative frequency components, respecitively. These are added in a way that does not change the API.

Fix autoscaling problem caused by axhline and axvline

Fix handling of c kwarg in scatter, with array of strings;
modification of patch by Ryan May. The fix involves making
cbook.is_string_like handle variables of type numpy.string_.

Clean up some of axes.psd() docstring. Add a reference to the psd_demo.py example.

Make iterable() and is_string_like() return True/False instead of 1/0.

Added import forgotten from previous commit

Fix a possible EINTR problem in dviread

Clarify hist docstring