Revert the --with-install-srcdir patch

Revert the --with-install-srcdir patch

Also, update description of debuginfo and sources to match
Debian and Red Hat more accurately, and move this sad tale
from INSTALL to etc/PROBLEMS which is a better home for it.
* Makefile.in (emacs_srcdir, install-c-src):
* configure.ac (emacs_srcdir, --with-install-srcdir):
* src/epaths.in (PATH_EMACS_SOURCE):
* src/lread.c (emacs-source-directory):
Remove.  All uses removed.
* lisp/emacs-lisp/find-func.el (find-function-C-source):
Do not worry about compressed C sources.
* src/lread.c: Do not include <dosname.h>.