Use last winnr instead of bufnr for LocateFile

Fixes issue where calling LocateFile from a split window with
`g:EclimLocateFileDefaultAction = 'edit'`
doesn't always open in the window you expect.

Repro:
- `:e A`
- `:vsp`; `<ctrl-w><ctrl-h>` (go to "left" window)
- `:e B`
- `:sp`; `<ctrl-w><ctrl-j>` (go to bottom-left window)
- `:LocateFile` etc.

Previously, when you select a file (with `<ctrl-e>`, or just using
the `DefaultAction` above) it would open in the top-left window,
even though you started in the bottom-left.

Please let me know if there are cases this breaks on
Merge remote-tracking branch 'dhleong/dhleong/UseWindowForLocateFile'