unix sockets: Linux is fine on any architecture

No need to limit ourselves to x86.
Regardless of architecture, sun_path is always 108 bytes long on Linux.

Signed-off-by: Jan Dvořák <mordae@anilinux.org>
unix sockets: reworked to support abstract namespace

Rewritten to read sligthly easier while adding support for abstract
namespaces on Linux.

Signed-off-by: Jan Dvořák <mordae@anilinux.org>
tests, doc edits, and minor changes for unix sockets
fix a bug in the syntax colorer
add a tag for secref to target
point from the 2d cond description to the keybindings docs
Use "Keyboard Shortcuts" as the tag to avoid breaking links
to the documentation

also, fix the deps
fix unstable/2d reader for ports with specials

(eg drracket files with comment boxes or images)
bring down below 102 cols
add a string constant for a menu item that just says "tab <i>"

(ie without a filename attached to it)
adjust tab menu items in drracket

specifically:
- make <menukey>-9 always go to the last tab
  (following chrome, as suggested by Jens Axel)
- make the <menukey>-1 thru <menukey>-9 menu items
  always be present in the menu, even when there aren't
  tabs, so that the shortcuts always appear taken
  (and so that cmd-4 never inserts a 4 into your buffer)
add c:s:pageup/down keybindings to move tabs around in a frame
racket/gui: default application-file handler requeues on active-frame change

When files passed to the default application-file handler cannot be delivered
because no frame is active or the frame does not accept files, then retry
when the active frame changes in the future (in addition to when the
application-file handler itself is changed).

This adjustment should fix a long-standing problem where files are
not delivered to DrRacket on Mac OS X.
Makefile: make PLT_SETUP_ARGS work more sensibly

Make sure it's at the end of the `raco setup` command line, and set
the executable name to "raco" instead of "raco setup" so that the `-l`
flag is effectively implied.
Allow re-definition at TR top-level
add a string constant to describe a new text color
allow 'text' as a possible category for colorizer results
adjust scribble lexer so that it uses the new 'text' category
instead of just using string

this is especially important for doing a good job with indentation
separate out state for spell checking string constants
from that for spell checking scribble {} content
add new menu item string constant