Rewriting the line-wrapping code to make use of the existing line-break code.

Rewriting the line-wrapping code to make use of the existing line-break code.
And undoing line wraps together with their causal text additions, and not as
separate actions because the user did not make them.
Patch by Mark Majeres.

git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@4945 35c25a1d-7b9e-4130-9fde-d3aeb78583b8