Prevent loading the same file twice

[adamk]

Whenever a file is being loaded, for any reason, the editor should ensure that it is not loaded twice.

Having two copies of a file in two editor tabs should be impossible to achieve.

[szabgab]

This used to be the case (there is a function Padre::Wx::Main::find_editor_of_file to help in locating the editor based on filename) The behavior was that when you tried to open a file that was already opened Padre simply focused on the already opened instance.

On the other hand there is a need to have the same file opened in the editor more than once (to edit on part of it while looking at another part) but in that case both editor windows should be tied to the same buffer. The "Split window" menu option used to offer this functionality many moons ago but then it got broken and recently removed.

[Sewi]

fixed in r8414, need to be verified under Windows

[Sewi]

Verified under windows (azawawi++)