OpenGl_ShaderManager::pointSpriteAlphaSrc() now does not return alpha from Red channel
for RGBA marker texture in Core profile.
OpenGl_ShaderManager::prepareStdProgramFlat() - restored code for drawing points without texture.
Built-in GLSL programs now flip .y in shaders instead of
relying on GL_POINT_SPRITE_COORD_ORIGIN unavailable on OpenGL ES.
Added sample markers.tcl (moved from test cases).
Sample now includes marker_kr.png for testing marker orientation.
