Fix the new lexer interaction when some of the lexer states were
finished, but not all. Don't re-do them the next time around

closes PR 13394
Fix sandbox doc example
win32: fix MinGW vs. MSVC build problem
at JPR's request: modified memq to return boolean and added memq? to teaching languages

the symmetry to member/member? suggested he is correct
docs: clarification for `immutable?'
fix non-JIT build

Fix a reference to a function that is only available when the JIT is
enabled.
tweak the latex rendering of ╔ and company
Fix type of `log-message`.
add rotary dial to the image guide
add some color to the image guide's fractals
and use local instead of internal define to
be more HtDP friendly
fix commit c818eb3ca3325fb7eac7f2a8105ea0121013214c

related to PR 13394
add `configure' test for mmap() and mprotect()

Use the test to enable execute permission on memory that is allocated
for code, including FFI callbacks.
fix typo in error message
racket/base: add exn:fail:filesystem:errno and exn:fail:network:errno

Provide raw error codes when available, which is mostly from filesystem
and networking primitives.
More precise return type for `magnitude' (it always returns nonnegative)
Moar `math/matrix' review/refactoring

* Gram-Schmidt using vector type

* QR decomposition

* Operator 1-norm and maximum norm; stub for 2-norm and angle between
  subspaces (`matrix-basis-angle')

* `matrix-absolute-error' and `matrix-relative-error'; also predicates
  based on them, such as `matrix-identity?'

* Lots of shuffling code about

* Types that can have contracts, and an exhaustive test to make sure
  every value exported by `math/matrix' has a contract when used in
  untyped code

* Some more tests (still needs some)
Added QR decomposition tests (mostly a pretty thorough randomized test);
fixed error in `matrix-cols-orthogonal?' revealed by testing
fix dist spec
New Racket version 5.3.1.12.
Disambiguate sentence on custodian shutdown.

See:
http://lists.racket-lang.org/dev/archive/2012-December/011373.html

Motivated by Sgeo's question in:
http://racket-lang.org/irc-logs/20121229.txt at 22:10.