adjust check syntax keyboard shortcuts

- make them use the same names as the context menu items
- add c:x;a to tack/untack arrows
Fix Guide typo

Closes PR 13695
add stub for enumeration support to Redex
fixing error message in rewrite-side-conditions.rkt
specified match precedence in lexer... hope I'm right
add an error check

related to PR 13346
fix typesetting for empty reduction relations

closes PR 13346
reference: expand notation section

Also, move it after the language-model section.
repairs for when set_locale() always return NULL

... as it does on Android
add GC-stress mode

Stress mode forces a GC on every N allocation attempts, and it makes
JIT-generated code always take a slow path.

This mode uncovered only a bad test case and some boring start-up
bugs (boring because start-up is deterministic enough that they
never happen), so far.
configure: fix `ar' and `as' inference for cross-compile
work around Android dlsym() bug
add advice on cross-compiling for Android
Fix require/untyped-contract to generate better names in contracts.

Related to PR 13716.
New Racket version 5.3.4.7.
added stepper-complete string constant
raco setup: add --doc-index; raco pkg: use --doc-index

This combination of changes moves the decision about rebuilding
"scribblings/main" and "scribblings/main/user" to `raco setup',
which is in a better position to know whether documentation should
be built at all.
Adding summary mode, quiet program mode and changing tests/eli-tester to cooperate so it adds useful information in summary mode
Clean up struct: and disallow unsupported options

Related to PR 13562
use correct value for (processor-count) on QNX