A fix for bug #467035 - this is a fairly major shift in

A fix for bug #467035 - this is a fairly major shift in
CSE processing. Previously when an operation was performed
before with the same operands then the result of the previous
operand replaced the result of the current operation entirely.
This was buggy , the current solution looks like a much cleaner
way to do things. Replace the current iCode with the an assignment
of the previous icode's result, we nolonger have to replace the
operands because the assignment exists, will have to watch for
performance regressions

git-svn-id: https://sdcc.svn.sourceforge.net/svnroot/sdcc/trunk/sdcc@1399 4a8a32a2-be11-0410-ad9d-d568d2c75423