Law student takes aim at Wilkerson... She is the daughter of immigrants. She is black and Hispanic. She is a single mother, and a Muslim. And, to the delight of the state party, Samiyah Diaz is also a Republican. The law student, who is collecting signatures to oppose state Senator Dianne Wilkerson, the Roxbury Democrat, in November, may have little chance of besting the 13-year incumbent. But for longtime Republicans, Diaz's candidacy is as much about shifting the image of the Republican Party as it is about winning. ''For the Republican Party, which needs to find some new energy on...