so move our BER API to the unused ober_* prefix to avoid some
breakage in ports.
Problem diagnosed by jmatthew with ber_free() in samba, but
there are many others as pointed out by sthen.
tests & ok rob
ok sthen (who had an almost identical diff for libutil)
"go head hit it" deraadt

snmpctl. Separate copies of ber.[ch] have existed and been maintained in sync
in ldap, ldapd, ypldap and snmpd.
This commit moves the BER API into /usr/lib/libutil. All current consumers
already link libutil. ldapd and snmpd regress passes, and release builds.
With help from tb@ and guenther@.
ok deraadt@, tb@

to control which symbols are exported from the shared library.
ok guenther@, deraadt@, jca@