support multiplication by constant negative integers
support multiplication by constant negative integers

this constmul code is still buggy though, so beware. mul by 7427 is currently
broken, for example. will fix it when I get a moment :)


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@21652 91177308-0d34-0410-b5e6-96231b3b80d8

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