Colon-separated lists in mpeu can't start with an empty string

[quantheory]

I found an old CESM Bugzilla bug noting that if you call get_indices_ from m_List, and the Values string starts with :foo, you get a weird error about how item oo was not found. This seems to be due to some oddity in the init_ method of that module.

Presumably, either starting with an empty string (i.e. the first character is a colon) should work, or there should be a somewhat better error message.