merge of r49785 (from branches/ggreif/use-diet): pass V to dyn_cast by const reference, this avoids copy-constructing and destructing all the time. especially important if these constructors are not accessible
merge of r49785 (from branches/ggreif/use-diet): pass V to dyn_cast by const reference, this avoids copy-constructing and destructing all the time. especially important if these constructors are not accessible

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@49787 91177308-0d34-0410-b5e6-96231b3b80d8

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