C-u C-SPC: doc string and behavior if mark = point

[Drew Adams]

1. Doc string for `set-mark-command':

"Set mark at where point is..." Should be "Set mark at point..." or
"Set mark where the cursor is..." Point is a position, and "at where"
is not correct English.

Split the run-on sentence that starts "With no prefix" at "; also".

Get rid of "e.g. C-u C-@". "Argument" and "prefix" alone should be
"prefix argument" everywhere. 

Don't speak of "a new position for mark". The mark is a (marked)
position, as far as users are concerned (yes, it also has buffer
info). "Point" and "mark" in the doc should stand for buffer
positions, not what is at those positions (e.g. the cursor).

Get rid of "With a double C-u prefix argument, e.g. C-u C-u C-@"; just
say "With `C-u C-u'".

Remove quotes around "region". Remove ", which is the closest
thing...". Remove the paragraph about setting the region altogether
(the region is not "set"). Just say "The region is the buffer area
between the mark and the cursor position. Some people call it the
"selection"."


2. In a buffer in which there is no mark, `C-u C-SPC' gives the error
"No mark set in this buffer". When point /= mark, the user sees the
cursor move. But when point = mark, there is no feedback. As an
enhancement, perhaps it would help to provide a message when mark =
point: "Mark removed at point". I don't know if this is a good idea,
but it can be disorienting when Emacs provides no feedback that an
action took place.


In GNU Emacs 22.0.96.1 (i386-mingw-nt5.1.2600)
 of 2007-03-21 on LENNART-69DE564
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4) --cflags -Ic:/g/include'