Skip test cases if the script or binary they need can't be found

mysql-test/mysql-test-run.pl:
  Move some opt_extern hacks to same place.
  Remove duplicate opt_skip_im=1 if opt_extern
mysql-test/t/fix_priv_tables.test:
  Skip test if $MYSQL_FIX_PRIVILEGE_TABLES is not set
mysql-test/t/system_mysql_db_fix30020.test:
  Skip test if $MYSQL_FIX_SYSTEM_TABLES is not set
mysql-test/t/system_mysql_db_fix40123.test:
  Skip test if $MYSQL_FIX_PRIVILEGE_TABLES is not set

mysql-test/mysql-test-run.pl

@@ -724,8 +724,6 @@ sub command_line_setup () {
   {
     $mysqld_variables{'port'}= 3306;
     $mysqld_variables{'master-port'}= 3306;
-    $opt_skip_ndbcluster= 1;
-    $opt_skip_im= 1;
   }
 
   if ( $opt_comment )
@@ -1235,6 +1233,7 @@ sub command_line_setup () {
   {
     # Turn off features not supported when running with extern server
     $opt_skip_rpl= 1;
+    $opt_skip_ndbcluster= 1;
 
     # Setup master->[0] with the settings for the extern server
     $master->[0]->{'path_sock'}=  $opt_socket ? $opt_socket : "/tmp/mysql.sock";
@@ -2011,10 +2010,7 @@ sub environment_setup () {
     $ENV{'MYSQL_FIX_SYSTEM_TABLES'}=  $cmdline_mysql_fix_system_tables;
 
   }
-  if (!$opt_extern)
-  {
   $ENV{'MYSQL_FIX_PRIVILEGE_TABLES'}=  $file_mysql_fix_privilege_tables;
-  }
 
   # ----------------------------------------------------
   # Setup env so childs can execute my_print_defaults

mysql-test/t/fix_priv_tables.test

 # Embedded server doesn't support external clients
 --source include/not_embedded.inc
 
+# Don't run this test if $MYSQL_FIX_PRIVILEGE_TABLES isn't set
+# to the location of mysql_fix_privilege_tables.sql
+if (`SELECT LENGTH("$MYSQL_FIX_PRIVILEGE_TABLES") <= 0`)
+{
+  skip Test need MYSQL_FIX_PRIVILEGE_TABLES;
+}
+
 #
 # This is the test for mysql_fix_privilege_tables
 # It checks that a system tables from mysql 4.1.23

mysql-test/t/system_mysql_db_fix30020.test

 # Embedded server doesn't support external clients
 --source include/not_embedded.inc
 
-# Windows doesn't support execution of shell scripts (to fix!!)
---source include/not_windows.inc
+# Don't run this test if $MYSQL_FIX_SYSTEM_TABLES isn't set
+# to the location of mysql_fix_privilege_tables.sql
+if (`SELECT LENGTH("$MYSQL_FIX_SYSTEM_TABLES") <= 0`)
+{
+  skip Test need MYSQL_FIX_SYSTEM_TABLES;
+}
 
 #
 # This is the test for mysql_fix_privilege_tables

mysql-test/t/system_mysql_db_fix40123.test

 # Embedded server doesn't support external clients
 --source include/not_embedded.inc
 
+# Don't run this test if $MYSQL_FIX_PRIVILEGE_TABLES isn't set
+# to the location of mysql_fix_privilege_tables.sql
+if (`SELECT LENGTH("$MYSQL_FIX_PRIVILEGE_TABLES") <= 0`)
+{
+  skip Test need MYSQL_FIX_PRIVILEGE_TABLES;
+}
+
 #
 # This is the test for mysql_fix_privilege_tables
 # It checks that a system tables from mysql 4.1.23