Update spec to 0.7. Remove obsolete/redundant rules for local variable initialization. Remove restriction on const instance creation. Liberalize type promotion rules.

R=rmacnak@google.com

Review URL: https://codereview.chromium.org//27054005

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@28589 260f80e4-7a28-3924-810f-c04153c831b5