Add reorder tabs facility in DrRacket
add keybindings for the tab movement keybindings

also move test case into an existing file because the test case
is short and it saves a little bit of trouble to have one fewer file
Fix collapse-newline in the case that the insertion point
is at the first position of the text.

closes PR 14043

Also, Rackety.
rename the preference drracket uses to remember the
teachpacks that were last selected by the user

This change is related to PR 14089 because that PR
made me realize that a similar problem happens with
this pref file. There is a simple fix, tho: just keep
the preferences for 5.3.6 and earlier using a different
key than the preferences for versions released after 5.3.6
adjust the way the header is saved in teaching language files
to match 5.3.6 and older versions

This is another problem introduced in 480afa4

closes PR 14089
fix some pkg tests
make the drracket/tool-lib library
exports and drracket:tool^ be in sync

This doesn't quite do the whole job
because something seems to get names
confused when structs and signatures
team up. This is a small example that, I
believe, demonstrates the problem:

(require racket/unit)

(struct p:s ())
(define p:struct:s struct:p:s)

(define-signature s1^
  ((struct s ())))

(define-signature s2^
  ((open (prefix p: s1^))))

(define-values/invoke-unit
  (unit (import s2^) (export))
  (import s2^)
  (export))
avoid invalidating the line numbers when doing things like drawing arrows in check syntax
disable test case
Rename some redex files
Move build-nt-property to separate file.
Cleanup preprocess-lang
Smarter production sort in redex nts
Add new test for redex production sort.

Running on the previous version caused unbounded recursion.
Fix typo in for documentation
Added pict to svg conversion. Added parameter to Scribble's html renderer to control choice between png and svg.
Small changes/fixes to rackunit.

* Make check params and exception stack trace only print in verbose mode.
* Add optional message for fail-check.
* Correctly shorten column name.