SES-1949 fix in commitInternal to make sure only executes the commit
when the current connection actually holds the transaction lock.
SES-1806 : Add null pointer exception for LiteralImpl.setLabel(null)
Merged in ses-1949 (pull request #212)

SES-1949 fix in commitInternal to make sure only executes the commit when lock acquired
SES-1806 : Change NPE to IAE for consistency with the rest of Sesame
Merged in SES-1806 (pull request #213)

SES-1806 : Add null pointer exception for LiteralImpl.setLabel(null)