Add texture bumpmapping feature.

minetest.conf.example

@@ -172,6 +172,8 @@
 # (1: low level shaders; not implemented)
 # 2: enable high level shaders
 #enable_shaders = 2
+# Set to true to enable textures bumpmapping. Requires shaders enabled.
+#enable_bumpmapping = false
 # The time in seconds it takes between repeated
 # right clicks when holding the right mouse button
 #repeat_rightclick_time = 0.25