* numeric.c (do_coerce): Add a warning when an exception is raised
  or an invalid value is returned in #coerce called by
  numeric comparison operators and the exception
  thrown by the caller has no information on the failure.
  In the next release such exception should not be rescued or
  should be the cause of the caller exception. nil is accepted
  as the "no possible coercion" return value. See #7688.
* test/ruby/test_numeric.rb: Add corresponding test.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46375 b2dd03c8-39d4-4d8f-98ff-823fe69b080e