if we're not inserting a file into a new buffer, partition the current

if we're not inserting a file into a new buffer, partition the current
buffer so that it's effectively a new buffer just before inserting the
file, and only restore placewewant afterwards; this is the same behavior
we would get if we opened the file, added all of it to the cutbuffer,
uncut at the current cursor position, and closed the file

git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@2062 35c25a1d-7b9e-4130-9fde-d3aeb78583b8