let "configure --disable-shared" work once again

Without this change, ./autogen.sh --disable-shared && make would
evoke a "can not build a shared library" failure for libvirtmod.la
due to the new use of libtool's -shared link option in
python/Makefile.am.  Now, --disable-shared also
disables building python.

* configure.in: Make --disable-shared imply --without-python and
silently override --with-python.
Improved by: Diego Elio Pettenò <flameeyes@gmail.com>

configure.in

@@ -1466,6 +1466,12 @@ dnl
 AC_ARG_WITH([python],
 [  --with-python              Build python bindings (on)],[],[with_python=yes])
 
+if test "$enable_shared:$with_python" = no:yes; then
+  AC_MSG_WARN([Disabling shared libraries is incompatible with building Python extensions.])
+  AC_MSG_WARN([Ignoring --with-python.])
+  with_python=no
+fi
+
 PYTHON_VERSION=
 PYTHON_INCLUDES=
 if test "$with_python" != "no" ; then
@@ -1813,7 +1819,6 @@ AC_ARG_WITH([qemu-group],
 AC_DEFINE_UNQUOTED([QEMU_USER], ["$QEMU_USER"], [QEMU user account])
 AC_DEFINE_UNQUOTED([QEMU_GROUP], ["$QEMU_GROUP"], [QEMU group account])
 
-
 # Only COPYING.LIB is under version control, yet COPYING
 # is included as part of the distribution tarball.
 # Copy one to the other, but only if this is a srcdir-build.