fix bug in getting "rest" of an integer-set
add test for integer-set:

- check that taking the rest of an integer-set results in a proper integer-set
one more integer-set test
Note that integer-sqrt produces exact output when given exact input.

Closes PR 9542.
Add reference to the DrRacket interface essentials from the Quick Start guide.

This adds a tag to DrRacket File menu docs.  It adds two margin notes
to the quick start, one linking to the essentials for using DrRacket,
and the other for saving Definitions.

Addresses PR 9501.
tweak
new simplified string constants; from Chongkai Zhu
fix the use of impersonator-ephemerons in the framework preferences library
Make struct types overlap with procedures.

Closes PR11971.
Add subtyping for Parameters.

Closes PR11992.
This required moving more stuff in to base-abbrev so that it could be
used in subtype.
Fix subtyping of invariant data structures.

Closes PR13521.
Make (Set a) a subtype of (Sequenceof a).

Closes PR13485.
Closes PR12615.
Make naturals be a sequence type.
New Racket version 5.3.3.5.
adjust docs example to use collection-file-path and
to say a little more about checksums
fix docs for `begin0'

It's body currently isn't an internal-definition position.
fix Guide spec for `when' and `unless'

Closes PR 13538
fix docs on `case'

The Guide was was out-of-date in several ways, and the Reference
didn't describe the dispatch-time guarantee.
Fix subtyping for Negative-Single-Flonum.
Filters for comparisons with inifinity.