Add some path searching for the ap{r,u}-config files. Also, pick up the correct version (e.g. apr-1-config).
Add some path searching for the ap{r,u}-config files. Also, pick up the
correct version (e.g. apr-1-config).

* serfmake:
  (class ConfigScript): new base class for -config scripts
  (class APRConfig, class APUCONFIG): set the class constant for the right
    script name.
  (class ConfigScriptNotFound): new exception when a -config cannot be
    found on the path.

jandre/serf,jandre/serf,jandre/serf,jandre/serf