[R6RS] Library / filesystem mapping

[R. Kent Dybvig]

> The most widely recognized extension seems to be
> ".scm".
> ...
> Just about any three-letter extension we choose will
> conflict with someone else's.  A Google search on
> 'file extension .scm' turns up 1,050,000 pages; the
> corresponding search for ".sch" turns up 741,000.

For completenes, 'file extension .ss" turns up 1,180,000 hits.  'file
extension .scm' actually turns up 1,150,000 for me, so .ss and .scm
are about as widely recognized.

> Kent's suggestion, ".sls", turns up 197,000 pages.
> If we're going to pick a new extension, I'd suggest
> ".slf" for "Scheme library file", which has only
> 44,500 page hits.

.slf is fine with me.

Another possibility is to allow any of serverai extensions including
at least .scm, .sch, and .ss.

Kent