Infinite line defined by two points

[stefanpetrea]

It would be useful to have the ability to build an infinite line that passes through two points.

Some people need find point that would lie on a segment's continuation(for example if they need to extend that segment indefinitely and see if it would hit a different geometry along the way, maybe a polygon). And currently it seems that the way this is done is ​by computing the segment's bearing and new length, and are extending their lines that way.

Since PostgreSQL has +/- Infinity ​described in the docs for floating point types, maybe those could be used to define such a line.