Moved VERSION into a single file

You can now update VERSION via just one file:
lib/net/ldap/version.rb

This makes maintenance easier.
Connection: Added support for failover

If multiple host-names (space separated) are passed in to the
configuration, then attempt to try them in order until one works
(success) or all fail (raise error).

The ports can similarly be passed in as a space delimited list as
well.
Merge remote-tracking branch 'docwhat/failover' into stable

* docwhat/failover:
  Connection: Added support for failover