Misc: OpenGL 3.0 compatibility & misc

- Fix OpenGL 3.0 compatibility by changing glFramebufferTexture() to
  glFramebufferTexture2D(). Thanks to danfe for suggestion!

- Add notification about DocBook toolchina dependencies. Thanks to
  danfe. (#121)

opengl.c

@@ -1035,7 +1035,8 @@ glx_blur_dst(session_t *ps, int dx, int dy, int width, int height, float z,
     if (!last_pass) {
       static const GLenum DRAWBUFS[2] = { GL_COLOR_ATTACHMENT0 };
       glBindFramebuffer(GL_FRAMEBUFFER, fbo);
-      glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, tex_scr2, 0);
+      glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
+          GL_TEXTURE_2D, tex_scr2, 0);
       glDrawBuffers(1, DRAWBUFS);
       if (glCheckFramebufferStatus(GL_FRAMEBUFFER)
           != GL_FRAMEBUFFER_COMPLETE) {