lib: Start removing use of deprecated NumPy API
lib: Remove use of deprecated NumPy API in pixops.hpp
lib: Also remove use of deprecated NumPy API in #ifdef HEAVY_DEBUG sections
lib: Avoid warning on void pointer aritmetics in pixops.hpp
lib: Disable deprecated NumPy 1.7 APIs for NumPy 1.7 forward
lib: Attempt to fix NumPy version detection
lib: Remove assert on pygobject-2.0 in SConscript

The PyGObject stuff for GEGL works fine without it.
gegl: Update code to work with gegl-0.3 (GEGL master)
brushlib/examples: Disable broken write_ppm functionality in minimal.c
Allow to enable OpenMP multithreading for Python-based surface

Has a huge critical section when retrieving tiles, but at least
allows for using multithreading for dab rendering.
gui: Initialize the BackgroundList on first window show, instead of on startup

Reduces the startup benchmark from about 2.1 seconds to 1.2 seconds on my machine.
Will likely give larger speedups for systems with less I/O bandwidth.
gui: Fix missing default background image on startup

Regression introduced in 6991eb1a5937ff553687d3f149cad5e6d005f8e9
Do it proper, instatiate BackgroundList always, but only load the
default background into the model at __init__ time, and provide
and API used by Window to load the rest upon 'realize'.
Now that I know what this affects, remove the exclamation mark
Merge branch 'mypaint-head', includes new OpenMP stuff. Enable with `scons enable_openmp=true`.

See also https://mail.gna.org/public/mypaint-discuss/2013-06/msg00001.html