Add test to mysql-test-run.pl to see if the udf_example.so is availble. Set envioronment variable UDF_EXAMPLE_LIB if it is.
Then check in have_udf if that variable is set. Finally use tahe variable when loading the shared library. 


mysql-test/include/have_udf.inc:
  Add check if udf_example.so(or similar) is available
mysql-test/lib/mtr_misc.pl:
  Add funcion "mtr_file_exist" to search for files
mysql-test/mysql-test-run.pl:
  Add checks to find the udf_example.so library
mysql-test/r/udf.result:
  Update result
mysql-test/t/disabled.def:
  Remove udf.test from disabled tests
mysql-test/t/udf.test:
  Use variable UDF_EXAMPLE_LIB when looking for shared library to load
mysql-test/r/have_udf_example.require:
  New BitKeeper file ``mysql-test/r/have_udf_example.require''