[tex-eplain] Position of optional argument

[Karl Berry]

    \definexref redefines \temp. It is generally inadvisable
    to use such a generic name for your own temporary macros.
    As far as I know, no macro package uses \my<anything>, so
    \mytemp would be better.

    On the other hand, general macro packages like eplain ought
    to avoid simple macro names like like \temp and \next (or
    even \cs (used in \@getoptioalarg), using instead something
    unlikely to be tried by a user.

I suppose, although it seems equally true that users should not assume
that such common cs's are preserved across macro calls, as with the
scratch registers.

But anyway, Oleg, maybe you can change Eplain's temp cs's to all start
with \@eplain or something?

Thanks,
Karl