fixing REL7_3_STABLE build issues

The attached (new) src/test/regress/expected/geometry_9.out, intended
only for the 7.3 stable branch, allows a clean regression pass on my
FC4 box. I called it that to avoid conflicts with other geometry_n files
on later branches.

The attached patch for contrib/seg/segparse.y allows a clean 7.3 contrib
build. The latter fix looks like one that should be made on the 7.4
branch also - man 3 errno on my box says:

errno is defined by the ISO C standard to be a modifiable lvalue of
type int, and must not be explicitly declared; errno may be a macro.

I'm not sure why 7.4 doesn't choke at the same place, but doing the
Right Thing (tm) should not hurt. In later branches the declaration is
gone altogether, so the problem has disappeared.

cheers

andrew