Fix replacing the right length of text matched from a regex; Add support for back references when replacing with regex; Improve the speed of replace all/replace in selection; Don't lose the selection range after replacing in selection

git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@581 ea778897-0a13-0410-b9d1-a72fbfd435f5