Point.is_collinear() should check for object types

This patch adds a minor fix to Point.is_collinear() so that if any other
geometric object is passed to it, it raises a TypeError.

For more background:
https://groups.google.com/forum/#!topic/sympy/vZxvnwemC4k
Merge pull request #7327 from amitsaha/point

Point.is_collinear() should check for object types