It has always seemed as if there were two Cheryl Wheelers, with fans of the New England songwriter relishing watching the two tussle for control of the mic. There is poet-Cheryl, writer of some of the prettiest, most alluring and intelligent ballads on the modern folk scene. And there is her evil twin, comic-Cheryl, a militant trend defier and savagely funny social critic. The result is a delightful contrast between poet and comic.But there is no way you can read about Cheryl and get a good picture of what she or her concerts are like. You have to see one. Do whatever it takes to get to her concert. You won't be sorry.