Allow plots with 0-length axes

Closes PR 14053
Avoid allocations in BSP build and pens/brushes; most 3D plots are 5%-15% faster
Weaken exception testing for DrDr
fix 2htdp/image for text-only mode and add a test case that
covers improvements from 8fb8f56
Improve DrRacket .plt installation functionality so that it prints
out the file it tried to unpack when it fails
fix scale so it cooperates with the dc's current transformation

closes PR 14424
Add output of a few front page examples in explanations.
Catch #:row-var parsing problems in TR

Closes PR 14434
Make parse-type errors align with new Racket style
Revert "Add output of a few front page examples in explanations."

This reverts commit a5bc367b89eb8fe5ce4f2b684fde6deb6d759bfb.
Add initial failing fair vec/e tests
Add cantor n-tupling vec/e with slow but correct decode
Implement efficient n-tupling decode (not very efficient tho...)
Explicitly distinguish between cantor and box pairing vec/e and list/e
Implement fast fair boxy list/e
Use mixed fair and finite list/e and delete unused test file
fix object/c & fields that just have to exist

closes PR 14437
Post-release version for the v6.0.1 release
Allow functions with rest args in with-handlers.
raco decompile: fix for `#%foreign`

Merge to v6.0.1