Factor out s:GetLists() and use that consistently also in SwapInsert().
Correctly merge g:default_swap_list with g:swap_lists.

So that lists with the same name do not create duplicates (which later lead to clash queries), but the (filetype-specific) latter one overrides the default. This allows to redefine a global swap list with a filetype-specific one.
Merge pull request #13 from inkarkat/swaplist-precedence

Swaplist precedence