Recreate pot and po files

Although we have already string freeze, we need to recreate the
translation files again.

* These changes remove the 'Ok', instead we will only have 'OK'
  One way of spelling removes the burden of translations.

* We introduced 'Trade' as engine string. This is most often already
  translated, so it was just uncommented most of the time.
translation-de: shorten mouse button names.
xgettext is utf8 safe now
Translations: Bump version number to 0.18
Merge remote-tracking branch 'mainline/master'

Conflicts:
	mods/default/languages/engine.pl.po
	mods/default/languages/xgettext.py
Update version number in pot and po files.
Fix flavor text for items in xgettext tool.

Fixes #492.
Merge remote-tracking branch 'mainline/master'

Conflicts:
	mods/default/languages/engine.ja.po
Only show one tooltip context at a time

Closes #491

Tooltips can either be in the context of the map (events and NPCs), or
in the context of menus. Menu tooltips will always take priority over
map tooltips.
Allow map events to trigger music changes

Closes #494
Merge remote-tracking branch 'mainline/master'
Merge pull request #496 from dorkster/music

Allow map events to trigger music changes
Merge pull request #495 from dorkster/bugfixes

Only show one tooltip context at a time
Merge pull request #484 from stefanbeller/master

Recreate pot and po files
Don't apply bonus_per_mental twice on healing and shielding