src/MANIFEST.in: don't include stuff outside src/sage

Author: tornaria

src/MANIFEST.in

@@ -1,6 +1,6 @@
 include VERSION.txt
 
-global-include *.pxi *.pxd *.h *.hpp
+recursive-include sage *.pxi *.pxd *.h *.hpp
 
 prune sage/ext/interpreters   # In particular, __init__.py must not be present in the distribution; or sage_setup.autogen.interpreters.rebuild will not generate the code
 prune sage_setup