qdirstat: update to 1.6

This is a stable release. It brings performance improvements, new features
and some bug fixes:
* Performance improvement while reading directories
* Vast performance improvement for huge directories (100.000+ entries in a
  single directory)
* New packages view
* New unpackaged files view
* New standard cleanup: Check File Type
* Support for excluding directories containing a file with a specific name
  or pattern.
* Greatly improved man page
* Some minor bug fixes.

(markd)