Not_contain should use strstr, not strcmp on strings. (bug 13632)

Not_contain should use strstr, not strcmp on strings. (bug 13632)

For Version 2.5.0, (same for previous version 2.4.2), in source file fccfg.c,
on line 700,

Original:
      ret = FcStrCmpIgnoreCase (left.u.s, right.u.s) == 0;

Should change to:
      ret = FcStrStrIgnoreCase (left.u.s, right.u.s) == 0;

I think this is just a mistake when copy-n-paste similar codes in the same
function. Apparently, return for "Not_contain" should be just the inverse of
"Contain", not the same as "Equal".