The gltestsrc element uses two shaders: color_shader and snow_shader.
Those are alternatively assigned to the SrcShader->shader pointer and
their reference was transferred to it. Only the SrcShader->shader was
unreffed (in _src_shader_deinit()) so only one shader was properly
freed, the other one was leaked.
Fixed this by giving an extra ref to SrcShader->shader and unreffing the
2 shaders in _src_smpte_free().
https://bugzilla.gnome.org/show_bug.cgi?id=766661
This makes gltestsrc work everywhere \o/
- workaround RPi returning invalid values for positive coords in the
checker shader
- reduce the number of iterations in the mandelbrot shader for gles2
https://bugzilla.gnome.org/show_bug.cgi?id=751540