When installing bison, create a symlink from bin/bison to bin/bison1875
that way ports that require bison1875 (ie: PostgreSQL 7.4+) can properly
detect this dependency. Given both bison's have the appropriate CONFLICTS
sections, this should be a big enough hint to users to move from
bison < 1.875 to something more recent. Bump port revision.
Pointy hat to: bison(1) authors for grammar incompatibilities