If you use vim ( http://vim.org ) you can wrap the whole document to 79 characters at once, pretty easily. In Normal Mode, this would do it:

Code:
:set tw=79
:set fo=t
1GVGgq
tw = textwidth, which we set to 79 characters per line.
fo = formatoptions, which are options that the gq command will enact; we set it to "textwidth".
1G takes the cursor to the first line.
VG line-selects until the last line.
gq auto-formats the whole document using formatoptions, which now includes textwidth.