[racket-dev] Scribble output changes

For HTML output, `racketblock' and `codeblock' now use a style that
discourages line wrapping. So, when you make code that is too wide, it
will usually[*] extend past the right margin instead of wrapping lines.
This doesn't mean that too-wide code is ok; it's just a better failure
mode in most cases.

                                    [*] Probably not for IE7 and earlier.


Latex output changed in more ways:

 * Documentation via `defform', `defproc', etc., renders with a
   vertical bar to the left, instead of a thin horizontal line above.
   (Thanks to an anonymous DLS'11 reviewer for this suggestion.)

   Also, those forms add vertical space like `codeblock', so they look
   right in document formats such as the SIGPLAN style.

 * Table content is vertically centered by default, making it more
   consistent with HTML.

 * In a table cell, a paragraph with a `#f' style name is rendered as a
   single line (as before), but a width is imposed on paragraphs that
   have a style name to make them flow as paragraphs.

 * More generally, a paragraph or nested flow can be "boxable", which
   means that it supplies a rendering mode (via a `box-mode' style
   property) such that the output is a Tex box instead of a paragraph.
   Box mode is triggered by cells in a multi-column table.

   The output from `racketblock' and `codeblock' is boxable, which
   means that tables and table columns containing code automatically
   size the expected way (i.e., like HTML). Meanwhile, outside of a
   table, boxable blocks render the old way, which allows page breaks
   within the block and generally cooperates better with Latex document
   styles.