this is a primitive, so it belongs in the 
    pdfTeX manual and not in anything from LaTeX.

We're still talking about \pdfstrcmp?  Paul Isambert, Thanh, Hartmut,
.., and I recently (Nov'10) released an update to the pdfTeX manual
which includes that, among other "missing" primitives which had been
implemented for years but never inserted into the doc.