graphics: fix cython 0.20 compilation. closes kivy#1796

Author: tito

kivy/graphics/instructions.pxd

@@ -7,7 +7,6 @@ cdef class Canvas
 cdef class RenderContext
 
 from vbo cimport *
-from context_instructions cimport *
 from compiler cimport *
 from shader cimport *
 from texture cimport Texture
@@ -58,6 +57,9 @@ cdef class ContextInstruction(Instruction):
     cdef void push_state(self, str name) except *
     cdef void pop_state(self, str name) except *
 
+
+from context_instructions cimport BindTexture
+
 cdef class VertexInstruction(Instruction):
     cdef BindTexture texture_binding
     cdef VertexBatch batch