more on file: URLs

[Shriram Krishnamurthi <shriram@cs.rice.edu>]

Okay, it's changed again, this time hopefully for the long haul ...

This is with reference to the URL library in the net collection.

The path section of a URL structure is now

- a path as per the RFC if the scheme is not "file"

- a platform-dependent path if the scheme is "file"

When combining URLs, you still use an RFC-style (slash-separated) path 
for the relative URL.  The benefit to this is that it allows a
consistent specification for both the Web and the local filesystem
(eg, the PLT documentation).

People using this code should be sure to read the documentation for
combine-url/relative, which is now quite elaborate.  Note especially
that this procedure can now (in rare cases) raise an exception.

I have also indexed documentation under the tag "file:", so if you
type that in Help Desk, you'll get some information on how to build
such a URL and what other documentation to read.

exp-tagged and released.  Please feel free to contact me with
questions and comments.

'shriram