bug#13949: 24.4.1; `fill-paragraph' should not always put the buffer as modified

[Jaakov]

Another implementation to fill paragraph in text mode could have as well 
scanned through the text linewise as suggested by Stefan Monnier.

I would implement just line splitting along the following idea for 
text-mode (not in LISP - please excuse me):

FOR EACH line l in the current paragraph
  REMARK space = whitespace or TAB
  c := rightmost column of l with space or -1 if none found
  IF c >= fill-column => 0 THEN
    REPEAT
      c' := c
      c := rightmost column of l|_{[0,c'[} with space
           or -1 if none found
    UNTIL c < fill-column
    IF c<0 THEN
      split line l at column c'
    ELSE
      split line l at column c
    ENDIF
    modifies := true
  END IF
END FOR

Of course, fill-paragraph needs to be much more than line splitting, so 
don't take my terrible piece of code too seriously, i.e., for anything 
except the initial idea.