Replace HTML entities in GridFieldAddExistingAutocompleter->doSearch() with actual charaters as the DropDown does not play nicely with HTML entities
disable source_file_comments in GridFieldAddExistingAutocompleter->doSearch() because they would be displayed as plaintext in the dropdown
Merge pull request #2650 from Zauberfisch/GridFieldAddExistingAutocompleter

Implove GridFieldAddExistingAutocompleter->doSearch() html output