Make generated contracts for Floats include NaN.

Closes PR13464.
Add extra tests for contract generation and float zeroes.
Add types for imaginary numbers and fix type of exact? and inexact?.
Don't special case typechecking of =.

Its type is more useful than the special typing rule.
Exclude the right zeroes when checking for equality.
minor cleanup
adjust raco test so it test the command-line
arguments to the empty vector before running anything
fix `regexp-match' variants given a long string and an output port

... again; commit d194fa6245 turned out to be incomplete.
dc<%>: fix baseline for slow-path non-combined text drawing

For example, fix baseline when drawing "a\u2144" with the
default fonr under Windows, where #\u2144 is subtituted from
another font.
racket/snip: make text snips accomodate height changes via substitution

Instead of assumning that the snip's text will match a font's height
metrics, check and remember the actual metrics if its doesn't match,
which accomodates font substitions (e.g., when using #\u2144 under
Windows).
new-style contract errors for `exn' field guards
racket/gui: add doc cross-reference
racket/gui/base: fix `menu-bar%' `get-frame' to return 'root

Return 'root istead of exposing the (hidden) root frame for
a menu bar that is shown when no frames are visible.
repair for snip% change

Fixes a problem with 755377ca82.
Use raco test by default
Add login link
Undo this for now
Using raco test by default, differently
Allowing PNR to decide which github checksum is used
adjust contour to track edit sequences better

Specifically when there is no delegate and an edit
sequence is started, track that differently in case
a delegate is set before the edit sequence ends
(in which case we don't want to end the edit
sequence in the delegate since we didn't start it
there)

related to PR 13491