Choice nodes may know that they are never not at the start of input.
This can remove start_of_input assertions in cases where they are statically known to fail.
The initial loop is unrolled once if the regexp might check for the start of input. Only the first iteration may be at the start, the following loop knows that it isn't.


git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1217 ce2b1a6d-e550-0410-aec6-3dcde31c8c00