wxpython: patch plot lib to work with newer numpy

Patches `wxPython/wx/lib/plot.py` to work with newer NumPy, e.g. 1.9+. See: http://trac.wxwidgets.org/ticket/16590

Fixes compile and runtime issues for applications that use `plot.py` [like GRASS 7.0](https://github.com/OSGeo/homebrew-osgeo4mac/issues/54) where it is used [in the `g.gui.iclass` module](http://grass.osgeo.org/grass70/manuals/g.gui.iclass.html).