build_search_command: exclude current folder from search result explicitly
In "Search" mode, when search result list contains the current directory itself, FileFormatData::FileFormatData() behaves badly because fl->priv->base_dir gets longer than dpath.
Anyway as "Search" mode GUI says "Look in folder:", it is guessable that the folder itself is not included in the result. Explicitly exlude the folder in SearchData::build_search_command().
Fixes #103 (closed)