python: install everythin into pyexecdir

Reported by Antoine Martin.

* python/Makefile.am: Here.
* NEWS: Mention the bug.

NEWS

@@ -206,6 +206,10 @@ New in spot 2.5.3.dev  (not yet released)
 
   Bugs fixed:
 
+  - Python *.py and *.so files are now always installed into the same
+    directory.  This was an issue on systems like Fedora that separate
+    plateform-specific packages from non-plateform-specific ones.
+
   - print_dot() will correctly escape strings containing \n in HTML
     mode.
 

python/Makefile.am

@@ -35,7 +35,7 @@ AM_CPPFLAGS = -I$(PYTHONINC) -I$(top_builddir) -I$(top_srcdir) \
 SWIGFLAGS = -c++ -python -py3 -O -nofastproxy -MD
 
 EXTRA_DIST = buddy.i spot/impl.i spot/ltsmin.i spot/gen.i
-nobase_python_PYTHON = \
+nobase_pyexec_PYTHON = \
   spot/__init__.py \
   spot/aux.py \
   spot/impl.py \