Michael Mayer / ctools

The processing for empty event files is skipped. The file is simply written out empty again.

Conflicts:
	ChangeLog
	NEWS
	src/ctbkgcube/ctbkgcube.cpp
	test/test_ctools.sh

…in case that those are not provided in the event list.

…response information in the XML observation definition file (when needed).

…alues to the vector when called several times)