Error message editing in backend/executor.

src/backend/commands/copy.c

src/backend/executor/execAmi.c

src/backend/executor/execGrouping.c

src/backend/executor/execMain.c

src/backend/executor/execProcnode.c

src/backend/executor/execQual.c

src/backend/executor/execTuples.c

src/backend/executor/functions.c

src/backend/executor/instrument.c

src/backend/executor/nodeAgg.c

src/backend/executor/nodeFunctionscan.c

src/backend/executor/nodeHash.c

src/backend/executor/nodeHashjoin.c

src/backend/executor/nodeIndexscan.c

src/backend/executor/nodeLimit.c

src/backend/executor/nodeMergejoin.c

src/backend/executor/nodeNestloop.c

src/backend/executor/nodeSetOp.c

src/backend/executor/nodeSubplan.c

src/backend/executor/spi.c