adjust drracket so check syntax can add its preferences itself

closes PR 13419
(cherry picked from commit 3e3283aeba1f239cc8722b4f13bfb19d48e8642e)
Removing exotic ports for PNRs
(cherry picked from commit b0f3f034122465bc7c115b3776ad400a68d690d1)
Disallow duplicate type variable declarations

Closes PR 13416

Please merge to 5.3.2
(cherry picked from commit 9c0a611b59d57548c0d0b527862f8a501a0098df)
scribble: add `+m' / `++main-xref-in' flag

The `+m' flag is a long-overdue shorthand for `++xref-in setup/xref
load-collections-xref', which links to installed documentation in
the same way as DrRacket's "Scribble HTML" button.

That is, use `+m' to link to installed documentation,

  scribble +m mine.scrbl

instead of the previously recommended

  scribble ++xref-in setup/xref load-collections-xref mine.scrbl

Merge to 5.3.2
(cherry picked from commit 3e8b6b98663386ea01a93f917ed328e8052c38d8)
Use correct contract for Procedure type

The only problem with this contract is that it does
not produce a very good error message
(cherry picked from commit 27d3042ad6008432428368bda882987f1f8a23c1)
Doc fix

Closes PR 13420

Please merge into 5.3.2
(cherry picked from commit 83766e1b118d19311990dfbd999f748ffcc5904d)
2012 -> 2013
(cherry picked from commit 79b9acd4443ae77a6f9bbaf28f9fb0dcc8e8a727)

Conflicts:
	src/worksp/gracket/gracket.rc
	src/worksp/racket/racket.rc
Update URLs again to r-l.o domain
(cherry picked from commit 9d4e47a96ec3dea51e5ea23c8317390b0c3aca6b)
pkg - Adding explanation of github supporting tags
(cherry picked from commit f3a3c64720f345ababe07d55818d5b32fdded2bf)
pkg - Improving error message on bad github urls
(cherry picked from commit 7cddc64e5ac797105047a8431f9739104aa9f15c)
Extending raco test to work on collections
(cherry picked from commit 3e0fff7dff8bc1b6bdd189dd52f3d5fab0ee9ae9)
test - Supporting packages in raco test
(cherry picked from commit 9015c15eec5a33783d4c0c6bd1b22f4852190b6e)
MPFR custodian shutdown procedure tries to clear the constants cache
even when MPFR isn't loaded; this should close PR 13423
(cherry picked from commit 441ad6eff42ae581deec8ea1990803753283f0ca)
Fix polydots

 - parsing of polydots values was fixed
 - certain polydots error cases are now reported
 - the custom application rule for values was fixed

Closes PR 13365

Please merge to 5.3.2
(cherry picked from commit f577b49a4df973aab1cfc8cdb45f93320637009d)
Change exception predicate for a test

For some reason, the other predicate breaks on some
test setups, even though it usually succeeds.

Please merge to 5.3.2
(cherry picked from commit c5c6280d8767a33891060c6d54907b2aafe778aa)
Use Racket lexer for code blocks.

Had been specifying Scheme lexer for code blocks, while waiting for
new Racket lexer to wend its way from Pygments to Pygments.rb to
Linguist to GitHub.

That day is almost here: Linguist will soon update and deploy to
GitHub.  And Racket 5.3.2 is about to release.  As a result, I think
this is the correct time to switch to the Racket lexer: It should be
live on GitHub by the time people are using Racket 5.3.2.

/cc @rmculpepper -- I think this commit should go into the 5.3.2
release.
(cherry picked from commit 4d3a5bad04d0958c71c70aaed0ab2c2055c5f272)
scribble/decode: fix contract on `decode-compound-paragraph'

Add a test suite that at least tries each export of `scribble/decode'.

Merge to v5.3.2
(cherry picked from commit 5ab048bb5cd05fa109b990bb73bc7033b09230ee)
scribble doc corrections

Merge to v5.3.2
(cherry picked from commit 5134bc0888c26c70bda83c607d73e530314cbbd8)