Export windows should offer a default filename with extension

[dstillman]

Save dialog should be pre-filled with something like export.xml, export.rtf, etc. At the moment it would be pretty easy for users to create extension-less files that they then can't open.

[simon]

actually, users should be able to open extension-less files (the import filters should all have detectCode), but your point is valid. the problem is, if the user switches the format, I can't switch the extension, because Firefox's save dialogs don't offer much in the way of functionality. should i presume that, if the user wants something besides the default export format, that he'll change the extension himself?

[dstillman]

(I meant if they try to open it elsewhere in the OS.)

Yeah, I guess just using the default and hoping they change it themselves if they use a different format is the best we can do--I notice that's what happens with Firefox's Save Page As dialog.

Annoying.

[simon]

(In [587]) closes #236, Export windows should offer a default filename with extension
closes #238, present dialog if no import translator is available for a file
closes #240, change XML namespaces