avoid internal error on misconfigured executable
racket/runtime-path: fix ".ss" vs. ".rkt" search for `lib` paths

The package split exposed another place where searching
is needed, because the fallback in `collection-file-path`
to `collection-path` didn't work after the split.
slideshow: fix clipping for 4-up mode and for printing
fix custodian-related memory-management problem

The problem mainly affected `register-custodian-shutdown`
from `ffi/unsafe/custodian`, which is used by `math/bigfloat`
and `ffi/unsafe/com`.

When a value is registered with a custodian, the value is held
weakly, but the shutdown procedure is intended to be held
strongly. At the C API level, the data associated with a shutdown
function pointer is intended to be held strongly.

A custodian itself, however, is retained weakly by other custodians
in its family, so that custodians can be GCed and their elements
transferred to a parent custodian. Since the custodian itself may
be held only weakly, the callback & data in a custodian was effectively
held weakly --- which, in turn, can break assumptions in code such
as `ffi/unsafe/custodian` that expects strong references to prevent
finalizers from running.

Fix the problem by registering a reference to callback data as
data in a custodian's finalizer, which makes the data strongly
retained no matter how the custodian is retained.
Fix `path-replace-suffix' and `path-add-suffix' on path for some system
Fix pkg documentation to reflect implementation.
Including test from PR14064
Moving planet-compat to S3
clean
Less output
Different email addr for nobody
S3 doesn't give up HTTPS, so turn it off
Initial pass at S3 version
Eval search on server, use hash, and only add once
cleanup
save settings in url
atom
attempting to deal with hash changes and giving up
conflicts as tags
info page template is ready