added the possibility to overwrite old xml summaries.
improved the readability of the tostring method of flow sinks/sources
removed an inconstancy in FlowSink/Source of how to return null fields
fixed: debug output could contain a flow multiple times
test to not analyse the methods separately
method are again analysed separately
changes sparks to CHA (problem with null field sources)
Merge branch 'unstable' of
https://github.com/secure-software-engineering/soot-infoflow-summaries.git
into unstable

Conflicts:
	src/soot/jimple/infoflow/methodSummary/SummaryGenerator.java
	src/soot/jimple/infoflow/methodSummary/util/InfoflowResultProcessor.java