- Add test case(execute perror)
  - Check if strerror has returned NULL and set msg to "Unknown Error" in that case
  - Thanks to Steven Xie for pointing out how to fix. 


extra/perror.c:
  strerror might return NULL on Solaris 2.8
mysql-test/mysql-test-run.pl:
  Add possibility to execute perror from test case
mysql-test/r/have_perror.require:
  New BitKeeper file ``mysql-test/r/have_perror.require''
mysql-test/r/perror.result:
  New BitKeeper file ``mysql-test/r/perror.result''
mysql-test/t/perror.test:
  New BitKeeper file ``mysql-test/t/perror.test''