Adjusted dm-core dependency to be ~>
Adjusted dm-core dependency to be ~>

* Also updated to use plain string ("0.9.7") where possible since it is
  alot easier to audit and find/replace.  Strangely enough its far
  easier to make mistakes with the constant because it's not easy to
  immediately see what the version dependency is.
* Fixed a few bugs that were assumptions made in sam/dm-core that
  will not longer be the case when dkubb/dm-core is merged into
  the mainline.

datamapper/dm-is-remixable