Smallcaps crashes with accented characters

[Peter Budny]

The smallcaps function will crash lilypond if you give it a string with accented
characters (and possibly other Unicode characters). This input reproduces the
problem reliably for me:

% -*- coding: utf-8 -*-
\version "2.10.0"
\relative c'' {
  c1^\markup { \smallCaps "Accented characters áé" }
}

If you remove the accented characters from the string, it works fine.