Import of multiple less files is broken

Since commit https://github.com/collective/collective.lesscss/commit/ec8334d6e5d3b477248930e9a74f2a468edfe5b6, we cannot `@import` multiple less files.

I even tried the example package mentioned in the documentation (https://github.com/sneridagh/example.bootstrap) to be sure. It works with `collective.lesscss` 1.2 but not with newer versions.

This is caused IMHO by the fact that the compiler doesn't have any "directory context" anymore to find the other files (as it now uses pipes instead of files to compile content).