Issue: PATHNAME-COMPONENT-VALUE (version 1)

[David A. Moon <Moon@STONY-BROOK.SCRC.Symbolics.COM>]

      When constructing a pathname from components, conforming programs
      must follow these rules:
  
      16. Any component can be taken from the corresponding component
      of another pathname on the same host and device.

A possible alternative that's worth considering is:

      16. Any component can be taken from the corresponding component
      of another pathname.  When the two pathnames are for incompatible
      file systems (in implementations that support multiple file
      systems), an appropriate translation occurs.  If no meaningful
      translation is possible, an error is signalled.  The definition
      of "appropriate" and "meaningful" is implementation-dependent.

This provides more useful behavior that conforming programs can 
depend upon, but the behavior cannot be as precisely specified.
A significant amount of the Symbolics Genera pathname facility is
related to this capability, and it's used a lot in heterogeneous
networks, so maybe this is a useful capability that ought to be
called for in the language.  The cost to implementors is small since
they could define "appropriate" and "meaningful" to be whatever is
easiest for them, if their users don't complain.