Improve configure script a little bit

- automatically find apxs in addition to apxs2. This should make it easier to configure on more systems
- include freetype2.m4. Otherwise ./autogen.sh already fails with missing macro.
- fail if no C++ compiler was found



git-svn-id: http://svn.openstreetmap.org/applications/utils/mod_tile@29422 b9d5c4c9-76e1-0310-9c85-f3177eceb1e4