make Meta-e work for editors defined with wait=false

[matthias314]

If in define_editor the keyword argument wait=false is used (the default value), then the edit function always returns immediately, without waiting for the editor to be closed. As a result, one cannot use Meta-e anymore to edit the current input in an external editor. For this to work, the edit call used under the hood would have to wait for the editor. This PR fixed this.

The solution I propose is to add a keyword argument wait to edit (for the filename-line-column version only). If it is set to true, then edit will wait for the editor to close, no matter which wait value was used in define_editor. If the wait argument for edit is false, then the value used for define_editor is taken.