Initialize offset to zero in FT2Font::make_open_args

Clang warns that it gets a garbage value on Python 2, since
mpl_PyFile_Dup expands to a function call that does not use &offset.
It seems that the value is not used on Python 2 but it doesn't
cost much to silence the warning.
Silence some writable-string warnings

Cast string constants explicitly to (char*) since the
method calls aren't going to modify the strings.
Check the return values of mpl_PyFile_DupClose
Remove dead assignment

The value initially assigned to pix was never used.
Remove dead assignments in _image.cpp
Avoid a null-pointer dereference in _tri.cpp

Found using the clang static analyzer:
if PyArray_ContiguousFromObject returns NULL,
PyArray_NDIM(x) causes a null-pointer dereference.
Initialize the states array with calloc in _macosx.m

To silence a warning about garbage data from the clang
static analyzer. Also check the calloc return value.
Release some unreleased objects in the macosx backend
Disable copying of C++ classes with nontrivial destructors

http://stackoverflow.com/questions/4172722/what-is-the-rule-of-three
Merge pull request #2991 from jkseppan/tidyup-ft2font

Silence some compiler warnings related to ft2font
Merge pull request #2992 from jkseppan/tidyup-misc

Remove a few dead assignments
Merge pull request #2997 from jkseppan/rule-of-three

Disable copying of C++ classes with nontrivial destructors
Merge pull request #2994 from jkseppan/macosx-fixes

Minor fixes in _macosx.m
Merge pull request #2993 from jkseppan/tri-null-pointer

Avoid a null-pointer dereference in _tri.cpp
Added functionality for plotting the actual violin bodies to violinplot.
Added ksdensity (KDE) function in mlab and adapted _axes violinplot function to accept new KDE.
Added basic violinplot demo in examples
Added statistics lines to the violinplot function.
Added horizontal violin plot feature compatible with means, extremas and medians.
Fixed bug for regression test #1181 in scipy unit tests; ksdensity is now referred to as gaussian_kde and exists as a class in mlab.
Fixed list comp position bug and updated examples
Reverted 69b304c.