Converted "udf_example.cc" to C, avoids C++ runtime lib dependency (bug#21336)


sql/Makefile.am:
  "udf_example.cc" converted to C, avoids C++ runtime lib dependency (bug#21336)
mysql-test/t/udf.test:
  "udf_example.cc" converted to C, avoids C++ runtime lib dependency (bug#21336)
sql/udf_example.c:
  Changes to be strict ansi, except long long