INSTALL: convert to '' quoting, drop blank line at end

INSTALL: convert to '' quoting, drop blank line at end

This is allowed by recent GNU Coding Standards changes, and
mirrors recent gnulib changes:
https://lists.gnu.org/archive/html/bug-gnulib/2012-01/msg00267.html
https://lists.gnu.org/archive/html/bug-gnulib/2012-01/msg00298.html

I've confirmed that after these changes, the INSTALL generated and
installed by autoconf matches the INSTALL.ISO in gnulib.

* Makefile.am ($(srcdir)/INSTALL): Match gnulib INSTALL.ISO.

Signed-off-by: Eric Blake <eblake@redhat.com>