The pendulum has swung again. After slumping Wednesday as investors digested minutes from the Fed’s January meeting, stocks got a boost Thursday on signs the economy may be poised to pick up after a winter slump. US manufacturing expanded at the fastest in nearly four years in February, a Markit survey said. And the Conference Board said its index of leading indicators posted a moderate gain in January. The market is now close to erasing all of its losses after a volatile start to 2014. Concerns about slowing growth in China and the health of the US economy had pushed the S&P 500 down almost 6% for the year by the start of February.