WASHINGTON - Months of tumultuous negotiations with the White House and GOP allies have brought the Senate's liberal lion, Edward M. Kennedy, to the brink of passing a bill to legalize up to 12 million unlawful immigrants. But his concessions to get there have alienated liberals who in the past have counted him as their strongest champion. A showdown test vote is scheduled today, and the Senate could pass - or reject - the bill by week's end. Traditional Kennedy allies are mystified and angry at the Massachusetts senator's willingness to accept Republican-backed measures such as subjecting illegal immigrants to...