Use different scheme to handle MSVC6

Use different scheme to handle MSVC6

Recent commit 0b08cab0fc46a5f381ca18a451f55cf12c81d966 caused a function
to not be compiled when running on MSVC6, and hence its callers needed
to use an alternative mechanism there.  This is easy enough, it turns
out, but it also turns out that there are more opportunities to call
this function.  Rather than having each caller have to know about the
MSVC6 problem, this current commit reimplements the function on that
platform to use a slow, dumb method, so knowing about the issue is
confined to just this one function.