fix #2313: bad entries in history search
fix #1737: do not try to open a null filename

The settings may initially contain a null filename.
fix #2316: race condition in LeastRecentlyUsedSet

removeAll() must be synchronized as well. Otherwise, the documentation
states that it uses a (unsynchronized) iterator to perform the removal,
which causes race conditions.
fix #2317: exception when backing up the phone

We do not need a cgeoapplication instance anymore when trying to perform
a backup.
Do not translate untranslatable strings