[tree-ssa] PATCH to represent column numbers using source_location

[Steven Bosscher]

> There is nothing here that is specific to tree-ssa
---- 8< ----
> It's a big patch with a big ChangeLog.

Two very good reasons to not include it on the branch.  In addition this patch
makes it harder to compare with mainline and to merge to the branch.

When 3.4 branches, perhaps this can go on mainline.  The tree-ssa branch is
not a "replacement mainline" for patches that are too late for stage 3.

Just my $0.02, of course.

Gr.
Steven