Allow more than one version of the same software

In SlapOS we do in fact support/allow different versions for different
dependencies, so there isn't a reason why this should be disallowed.

nxdbom/__init__.py

@@ -83,7 +83,7 @@ def bom_software(installed_software_path): # -> {} (name,kind) -> PkgInfo
 
 
         info = PkgInfo(name, ver, kind, url)
-        bkey = (name, kind)
+        bkey = (name, kind, ver)
         if bkey in bom:
             assert bom[bkey] == info,  (bom[bkey], info)
         else: