By Trevor Hunnicutt NEW YORK, Nov 22 (Reuters) - U.S. fund investors pumped millions into bond funds for a 50th straight week, the Investment Company Institute (ICI) said on Wednesday, showing that caution in recent weeks may not portend a flight from debt generally. Taxable-bond mutual funds and exchange-traded funds (ETFs) took in $839 million during the turbulent week ended Nov. 15, the lowest in nearly a year, as high-yield debt came under pressure, according to the trade group.