Re-enable running the 'client_test' test case during release builds on the platforms (bug#7909).

mysql-test/mysql-test-run.sh:
  In a release build on the platforms, TESTS_BINDIR needs to be set to $BASEDIR/tests because the test 
  program 'client_test' is expected there (see 'client_test.test' with its 'exec', bug#7909).
  In an installation, TESTS_BINDIR needs to be set to $BASEDIR/bin because some NDB programs are 
  located there (see Jonas Oreland's change labeled '1.220, 2005-01-04 08:15:30+01:00').
  This patch is to unite these conflicting requirements.

mysql-test/mysql-test-run.sh

@@ -538,7 +538,12 @@ else
    MYSQLD="$VALGRIND $BASEDIR/bin/mysqld"
  fi
  CLIENT_BINDIR="$BASEDIR/bin"
- TESTS_BINDIR="$BASEDIR/bin"
+ if test -d "$BASEDIR/tests"
+ then
+   TESTS_BINDIR="$BASEDIR/tests"
+ else
+   TESTS_BINDIR="$BASEDIR/bin"
+ fi
  MYSQL_TEST="$CLIENT_BINDIR/mysqltest"
  MYSQL_DUMP="$CLIENT_BINDIR/mysqldump"
  MYSQL_BINLOG="$CLIENT_BINDIR/mysqlbinlog"