Merge pull request #293 from lissyx/revert-bug931718

Revert "Merge pull request #292 from lissyx/bug931718"
Bug 931718 - Fix XULRunner SDK path detection

With bug 906316 we are now able to have multiple versions of the SDKs on
disk, to avoid always re-downloading them. Path has changed, and we need
to be more clever to detect the actual SDK paths that are possibles.