Add prefix option to anchor string generator

Change-Id: I27f181645a12b7f711507091bb4194c8fdbdbcab
BaseX: Handle outdated index

Prints a warning to the debug log, if elements from the index can
not be found in the database.

Change-Id: Iffebe9c7632daec7f87e8010f7805af1338d895c
Merge "Add prefix option to anchor string generator"
Merge "BaseX: Handle outdated index"