Properly assign heapobject to constant functions.

R=jkummerow@chromium.org

Review URL: https://chromiumcodereview.appspot.com/17406009

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15245 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Let NaN flow as double into HBranch + some minor improvements

BUG=
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/17082003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15246 ce2b1a6d-e550-0410-aec6-3dcde31c8c00