Ruby

• ext/dbm/extconf.rb: don't check libdbm. It is not a ndbm
  implementation. (libdbm in Version 7 Unix is database library
  for single database per process.)

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@34666 b2dd03c8-39d4-4d8f-98ff-823fe69b080e