rackunit: make check-exn/check-not-exn raise error if given a non-thunk

Previously, (check-exn exn? 'foo) would pass even though 'foo is not a
thunk.  Now it raises an exn:fail:contract? exception.

Previously, (check-not-exn 'foo) would produce a check failure.  Now it
raises an exn:fail:contract? exception.
racket/gui gtk: make keyboard focus work in floating frames
raco expand & decompile: add `--columns` option
racket/gui cocoa: remove `warp-pointer` delay

Change suggested by Philipp Dikmann.
adjusted arg to raise-argument-error to produce sensible error msg
scribble: add `--html-tree <n>` mode for rendering to depth <n>

Depth 0 is the same as `--html`, depth 1 is the same as `--htmls`,
and higher depths cause sections and subsections to be rendered
into separate directories when they have their own pages.
scribble HTML rendering merges `style` attributes

This change fixes using `color-property` and `background-color-property`
at the same time, for example.
scribble/manual: generalize `deprecated`
adjust docs on `collection-path`

Use the `deprecated` function, and rephrase in terms of the collection
search path.
distro-build: recognize timeout and exceptions as failure
fix def/c macro to use pub again
make snapshot-site: better failure display & linking

Make the "current" links more stable by linking to the most
recent success when a build fails.

Also, add links to the build logs.
adjust default autosave delay to 30 seconds (down from 5 minutes)
Typo.
Add `module*' to syntax/parse's kernel-literals.
Add missing core form.
Have optimizer ignore contract definitions.

This bug was hidden by a bug in syntax/parse.
Have optimizer ignore #%top expressions.
Render scribble doc examples in the page
fix some misleading error messages

The misleading message that dropped submodule paths.