cps-ir: Implement boolean conversion in and use it to implement '&&', '||', and '?:'.

R=sigurdm@google.com

Review URL: https://codereview.chromium.org//737353002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41884 260f80e4-7a28-3924-810f-c04153c831b5
Add Link.copyWithout.

R=johnniwinther@google.com

Review URL: https://codereview.chromium.org//744023002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41885 260f80e4-7a28-3924-810f-c04153c831b5