Author: Dongsheng Cai
MDL-26388, pop up a dialog when attaching a file already being used in draft area.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=f392caba154764f0afce93de3b544508b88be2ba
http://github.com/moodle/moodle/commit/f392caba154764f0afce93de3b544508b88be2ba
+ 2.1dev en [fileexistsdialog_editor,core_repository]
+ 2.1dev en [fileexistsdialog_filemanager,core_repository]
+ 2.1dev en [fileexistsdialogheader,core_repository]
+ 2.1dev en [overwrite,core_repository]
+ 2.1dev en [renameto,core_repository]