Log Message:
Fix commit involving Makefile:1.2 that bumped the PKGREVISION of
merb-sequel to 1.  In that commit, the dependency was bumped at the
package level, but gems also track dependencies independently of
pkgsrc, so patch the Rakefile to:

+ Bump the dependency on sequel to 1.4.0.
+ Remove the dependency on sequel_model, which was merged into the
  main sequel package as of version 1.4.0.