Don't install the unwashed masses of Guile header files in the

Don't install the unwashed masses of Guile header files in the
main #include path; put most of them in a subdirectory called
'libguile'.  This avoids naming conflicts between Guile header
files and system header files (of which there were a few).
* Makefile.in (pkgincludedir): Deleted.
(innerincludedir): New variable; this and $(includedir) are enough.
(INCLUDE_CFLAGS): Search for headers in "-I$(srcdir)/..".
(installed_h_files): Divide this up.  Now this variable lists
those header files which should go into $(includedir) (i.e. appear
directly in the #include path), and ...
(inner_h_files): ... this new variable says which files appear in
a subdirectory, and are referred to as <libguile/mumble.h>.
(h_files): List them both.
(install): Create innerincludedir, not pkgincludedir.  Put
the installed_h_files and inner_h_files in their proper places.
(uninstall): Corresponding changes.
* alist.h, append.h, arbiters.h, async.h, boolean.h, chars.h,
continuations.h, debug.h, dynwind.h, error.h, eval.h, fdsocket.h,
feature.h, fports.h, gc.h, genio.h, gsubr.h, hash.h, init.h,
ioext.h, kw.h, libguile.h, list.h, markers.h, marksweep.h,
mbstrings.h, numbers.h, options.h, pairs.h, ports.h, posix.h,
print.h, procprop.h, procs.h, ramap.h, read.h, root.h,
sequences.h, smob.h, socket.h, srcprop.h, stackchk.h, stime.h,
strings.h, strop.h, strorder.h, strports.h, struct.h, symbols.h,
tag.h, throw.h, unif.h, variable.h, vectors.h, version.h,
vports.h, weaks.h: Find __scm.h in its new location.
* __scm.h: Find scmconfig.h and tags.h in their new locations
(they're both "inner" files).