Displaced Chinese Ancestors Reburied in U.S.
Thousands of deceased Chinese are being exhumed by their descendants and reburied in America, often in places they have never visited in life; descendants fear destruction of their ancestors' graves as cemeteries in China are bulldozed to make way for farms, offices and housing tracts; posthumous emigration reverses tradition that dates to gold rush, when Chinese-American would dig up laborers who had perished in California and ship them back to their ancestral villages; photo (M)