Repair regression in "make replace" in DESTDIR case.

"make replace" is defined to replace a package with a newer version,
and update depdending packages to depend on the new version.  It has
long been understood that this is not always safe, with the responses
being "tell people to be careful" and the unsafe_depends variable
scheme and pkg_rolling-replace.  In the DESTDIR case, make replace is
implemented by pkg_add -U.  Usually, this is fine - even if the
ABI/shlib majors have changed, the package is replaced, and then a
later make replace of unsafe_depends=YES packages, either manually or
via pkg_rolling-replace, will bring the system to where it should be.
However, there are pinned dependencies on osabi where the depending
package will not accept the new version, and that causes pkg_add -U to
fail.  This is incorrect, as a) those packages don't depend on the
osabi exact version any more than packages depending on jpeg depeend
on the particular shlib major, yet jpeg dependencies aren't pinned.
And, osabi changing version is not necessarily an ABI change -
consider 5.0_STABLE just before 5.1RC1 and just after, where only the
version string changed.

Therefore, add -f to pkg_add -U so that the update will succeed.


(gdt)