Improve Quickfix window detection

When using a non-english locale, the name of the Quickfix window can change, making the detection of Quickfix vs Location list fail.
E.g., my locale is set to italian and the Quickfix window's name is `[Lista Quickfix]` rather than `[Quickfix List]`.
This change generalizes the pattern used to detect the Quickfix window.
Merge pull request #656 from michamos/patch-1

Improve Quickfix window detection