Fix TM directory creation: create just the parent dir.

Lucene doesn't like it when the index directory already exists, without data.
Fix catching of Lucene exceptions in Preferences.
Fix multiple Find windows.

Fix the code for maintaining single Find window.  Rather that look it up
by name, use proper code for keeping track of the singleton.  The former
was broken by something, presumably some change in wx, and rather than
hunting the exact cause down, it's faster to do it properly (as it
should have been done in the first place).
Use a splitter instead of hard-coded ratio in the catalogs manager.
And Windows manifest, declare Win 8.1 compatibility in it.
Add native OS X Edit menu items.

Also move editing items closer to the top of the menu, leaving Find
together with other standard items at the bottom.
Update Basque translation.
Fix file permissions on *.po files (no exec bit).
Update Portuguese translation.
Fix crash after attempting to read an invalid file.
Fix OS X menu tweaks to work even without the Find menu item.

(Such as when not showing any windows.)
OS X: fix quitting logic to work without windows.
Update Vietnamese translation.