Reviewed by Maciej Stachowiak

Pull local and constant initialisation out of slideRegisterWindowForCall
and into its own opcode.  This allows the JIT to generate the initialisation
code for a function directly into the instruction stream and so avoids a few
branches on function entry.

Results a 1% progression in SunSpider, particularly in a number of the bitop
tests where the called functions are very fast.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@36695 268f45cc-cd09-0410-ab3c-d52691b4dbfc