Resolve "Attached (text) files open with different name"
In order to present the file name "as is", it makes evince store
its temporary attachment inside a evince.XXXXXX
subdirectory
instead of the previous approach of concatenating XXXXXX to the
file name, which overrided the extension.
From the user's point of view, when opening the attachment, the filename will have the same as displayed in Evince, which is what the user likely expects.
https://bugzilla.gnome.org/show_bug.cgi?id=772188
Fixes #711 (closed)
Closes #711 (closed)