SES-1947 : Clarify javadoc for deprecated RDFParser.setStopAtFirstError

Clarification is that the easiest way is to use addNonFatalError
SES-1947 : Link stopAtFirstError to non-fatal errors

This restores the behaviour of the deprecated RDFParser.stopAtFirstError
function if the new functions are never used. If the new functions are
used, in particular, setNonFatalErrors(emptySet), then there may be a
discrepancy.

This commit is only aimed at restoring the previous behaviour for users
who are not migrating away from the deprecated functions from 2.7
SES-1847 : Make verifyData not always return true
SES-1847 : Simplify setVerifyData
SES-1847 : Extend coverage of ParserConfig unit test
SES-1947 : Handle multiple calls to setStopAtFirstError correctly
Merged in SES-1947 (pull request #211)

SES-1947 : ParserConfig.stopAtFirstError always returned true