Added test case for checking the return code when an xid does not exist.
Added test case for checking the return code when an xid does not exist.

zapov/pgjdbc,marschall/pgjdbc,phillipross/pgjdbc,AlexElin/pgjdbc,zapov/pgjdbc,golovnin/pgjdbc,sehrope/pgjdbc,zemian/pgjdbc,whitingjr/pgjdbc,Gordiychuk/pgjdbc,marschall/pgjdbc,zemian/pgjdbc,AlexElin/pgjdbc,jkutner/pgjdbc,lonnyj/pgjdbc,lordnelson/pgjdbc,ekoontz/pgjdbc,schlosna/pgjdbc,phillipross/pgjdbc,jorsol/pgjdbc,lordnelson/pgjdbc,panchenko/pgjdbc,jorsol/pgjdbc,golovnin/pgjdbc,whitingjr/pgjdbc,lonnyj/pgjdbc,rjmac/pgjdbc,sehrope/pgjdbc,panchenko/pgjdbc,jorsol/pgjdbc,bocap/pgjdbc,rjmac/pgjdbc,rjmac/pgjdbc,Gordiychuk/pgjdbc,bocap/pgjdbc,golovnin/pgjdbc,underyx/pgjdbc,amozhenin/pgjdbc,panchenko/pgjdbc,davecramer/pgjdbc,marschall/pgjdbc,lordnelson/pgjdbc,davecramer/pgjdbc,zapov/pgjdbc,Gordiychuk/pgjdbc,zemian/pgjdbc,davecramer/pgjdbc,bocap/pgjdbc,jamesthomp/pgjdbc,jamesthomp/pgjdbc,amozhenin/pgjdbc,jorsol/pgjdbc,pgjdbc/pgjdbc,whitingjr/pgjdbc,pgjdbc/pgjdbc,marschall/pgjdbc,schlosna/pgjdbc,ekoontz/pgjdbc,pgjdbc/pgjdbc,amozhenin/pgjdbc,AlexElin/pgjdbc,underyx/pgjdbc,jkutner/pgjdbc,davecramer/pgjdbc,alexismeneses/pgjdbc,jkutner/pgjdbc,underyx/pgjdbc,alexismeneses/pgjdbc,sehrope/pgjdbc,jamesthomp/pgjdbc,pgjdbc/pgjdbc,sehrope/pgjdbc,phillipross/pgjdbc