Avoid feeding inexact numbers to random while generating contract-satisfying values.

Also fix a minor doc error.
Fix type in docs.
Keep dead case-lambda clauses around to avoid changing arity.

Closes PR14468.
Proper indentation for syntax-parse in DrRacket.
redex: don't treat _ as a binder in extract-names

Closes PR 14466
redex: allow named ellipses to be bound as term-ids.

This enables the internal bindings generated by where clauses.

Closes PR 14467
Revert edit to expected result.
redex: fix _ docs typo
Fix apply with (Listof A) args.

Closes PR 14465.
Add a test suite for infer.
configure: add --enable-sysroot

The `--enable-sysroot` flag simplifies an Android cross-compilation,
for example.
ARM JIT: fix software floating-point

I broke uses of LDRD and STRD when compacting the set of registers
used by the JIT. The LDRD and STRD instructions are given one
register explicitly, but they implicitly use the next regsister, too,
and the specified register must be even-numbered. Lining up a pair of
registers requires a little shuffling before and after the operation.

Also, the LDRDI and STRD encodings were broken, and the inlined
fl->fx conversion was not right.

Closes PR 14470
no getprotobyname on Android
improve random contract generation

notably enable the generator to actually use things from the
environment but currently only when they are directly in the
environment so, eg:

   (-> (-> is-eleven?) is-eleven?)

can't be generated (since the contract system doesn't know
about is-eleven? and also doesn't yet know that it can call
the argument thunk)
improve or/c random generation and get rid of old, not-working
generation for the old-style -> contracts
revise error printed for kernel-/debugger-sent SIGSEGVs
fix clean-up handling for the main thread of a terminated place

This bug might be reposnible for the occassional crashes seen in
DrDr for the easter-egg test.

Merge to v6.0.1
racket/base: add `string-port?`
file/zip: recognize string ports as seekable
fix 'planet remove' commandline argument checking