Fix syntax/c. Closes PR13447.
fix to use compiled startup code
repairs to extflonum changes
adjust randomized racket machine tests to print to
stderr on failure and to not print anything on success
Fix type of quotient on fixnums.

Closes PR13466.
Improve type of exact? and exact->inexact.

Adapted from a pull request by Eric Dobson.
Fix test for invalid fixnum quotient optimization.

The test depended on fixnum width, which is not portable.
added union-find to the data collection
another repair for extflonum support
fixes the responsiveness optimization disabled in
c8bee5acf76e4257a688e0bf2712e51404bd5048
improvements to union find suggested by Sam and Danny
fix the random property; sadly still doesn't find the bug Danny found
guard a call to invalidate-bitmap-cache in
check syntax so it only happens when something
would draw differently
web page: videos link and other small changes
fix bug in commit 4c4161ce2bb6ca3e81282d0df27b916349b64a84
bring back the syncheck:add-rename-menu method in a way
that preserves backwards compatibility for the
drracket/check-syntax library
fix some bugs in union-find

(thanks to random testing)
unbreak drr
adjust check syntax so it highlights all identifiers with the same
binding site (with a green/yellow bubble) when the mouse moves over
any one of them

This change comes about because of the recent fixes to the
interactivity wrt to the rename menu. Basically, in order to fix the
bug (but still preserve the interactivity optimization), check syntax
changed from sending the information "here is a place to offer a
rename for these identifiers" to "here is a set of identifiers that
are all free-identifier=?" (the difference being that the latter does
not imply you got them all (which enables the optimization) and that
the information is slightly less rename-menu specific (which enables
the change in this commit))
Rackety