Fix some INSTALL.txt typos
snapshot management: add "current" link
move configuration-file info from "INSTALL.txt" to "pkgs/distro-build"
fix GC bug in FFI

A foreign procedure's data could get GCed before the procedure
was called, if the procedure is not otherwise reachable.

(Bug found by running tests in GC-stress mode.)
fix an FFI test case
fix GC bug

This is a variant of the bug fixed in
49fbca5b1830bc4bddb8522d7647518227a32dd0,
where a GC-notification callback still
could cause problems in a GC during a finalization
callback.

(Bug found by running tests in GC-stress mode.)
Update DrDr documentation with the correct command.
Run the net tests under `raco test`.
bring down below 102 columns
add gui-test pkg
get framework tests running again
fix c:c;c:e for empty sequences

closes PR 13905
bring down below 102 columns
snapshots: access current installers via "current" path
adjust the collection sorting that 'raco setup' so that it works
in our new pkgs world (and has a, hopefully, similar effect)
unbreak drracket
Split redex enumeration code into multiple files.