Fix namespace list order

Runtime namespace lists were being expanded by adding list members to the end of the runtime ordered dict, which broke repeat-section override for list members (by overriding the intended override with the original), e.g.:
```
[runtime]
   [[m1,m2,m3]]
        title = the quick brown fox
   [[m2]]
        title = jumped over the lazy dog
```
(this should result in ```m2``` getting ```title = jumped over the lazy dog```).

This change fixes the problem by replacing the original dict with an expanded one with the right order (simpler, and in any case ordered dicts don't have an insertion method).
`if ',' in key:` should be faster.