per DB's patch, overhaul the rcfile and history file reading and writing

per DB's patch, overhaul the rcfile and history file reading and writing
routines to fix a few fundamental problems and limitations; also add
getline() and getdelim() equivalents adapted from GNU mailutils 0.5 (and
tweaked to better integrate with nano), since the patch uses getline()

git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@1900 35c25a1d-7b9e-4130-9fde-d3aeb78583b8