Switch obvious clients to Twine instead of utostr (when they were already using

a Twine, e.g., for names).
 - I am a little ambivalent about this; we don't want the string conversion of
   utostr, but using overload '+' mixed with string and integer arguments is
   sketchy. On the other hand, this particular usage is something of an idiom.

llvm-svn: 77579