#137 Auto-select search string in search dialog

When I compare two files side by side, and use 'Find', the search dialog comes up with the previously-searched text. This text is not selected, so if I open the search dialog and immediately type the search string, my search string gets appended to the previously-searched text.
It is common in Search dialogs to have the text automatically selected; this way, I can type a new search string immediately, and it will replace the previous string.