The format previously included relative paths in the syntax
of the platform used to run `raco setup'. While a "cache.rktd"
built on Unix would work for Windows, the reverse would not
be true. Also, `raco setup' under Windows would get confused
because it would arrive at different relative paths for the
same collection (e.g., "drracket/private" and "drracket\\private").
The portable representation of relative paths is also
normalized.
A "cache.rktd" file still has absolute paths for Planet packages
or links installed with `raco link', but that's not a problem for
packaging a distribution with a portable "cache.rktd".
Also, `raco setup' cleans "cache.rtkd" by removing collections
that are omitted and by not including collections that have no
"info.rkt"/"info.ss" file.
including adding some uses of `with-module-read-parameterization'
so that `read-accept-lang' is set right anyway; still, so many
many places just set `read-accept-reader' to #t that making
`read-accept-lang' #f by default looks like too big of an
incompatibility
