LONDON (Reuters) - BlackRock Investment Institute (BII) predicted on Tuesday that developed market government bond returns would be negative over the next five years and raised its outlook on credit to "modestly overweight" on extraordinary central bank measures. "Developed market central bank actions should pave the way for lower volatility in interest rates, providing a stable environment for credit spreads to narrow," said BII head Jean Boivin, adding the backdrop for credit was now..