Update mirall_de.ts

Typo
Fixed parent folder detection if sibling directory starts with same name

Since `cleanPath` removes all the trailing slashes (https://qt.gitorious.org/qt/qt/source/84bfbd4cb090f7f77ae3b04308726d2b8ddf4792:src/corelib/io/qdir.cpp#L2118) the check at line 138 wrongly assumed that

`D:\Test` is a parent folder of `D:\TestFoo`.
Merge pull request #1292 from Pro/master

Corrected typo and fixed parent folder detection