Memory leak on searches

Memory leak when searching. Only tested on Qt Creator 2.5.0 but it may be on the later versions as the changelogs don't mention anything.

Steps to reproduce:
1. Search file system/directory with a lot of files for common strings or even just 1 character.
2. Watch memory usage go up. This is ok since there are a lot of matches to keep track of.
3. Clear the search results (doing a new search does nothing as it keeps the old search matches in history)

Expected result: memory usage should go down

Actual result: 5 GB memory leak