MEDIUM: checks: Make post-41 the default mode for mysql checks

MySQL 4.1 is old enough to be the default mode for mysql checks. So now, once a
username is defined, post-41 mode is automatically used. To do mysql checks on
previous MySQL version, the argument "pre-41" must be used.

Note, it is a compatibility breakage for everyone using an antique and
unsupported MySQL version.
diff --git a/reg-tests/checks/mysql-check.vtc b/reg-tests/checks/mysql-check.vtc
index 061f2c1..5344d95 100644
--- a/reg-tests/checks/mysql-check.vtc
+++ b/reg-tests/checks/mysql-check.vtc
@@ -89,13 +89,13 @@
     backend be2
         log ${S2_addr}:${S2_port} daemon
         option log-health-checks
-        option mysql-check user user
+        option mysql-check user user pre-41
         server srv ${h1_mysql1_addr}:${h1_mysql1_port} check inter 1s rise 1 fall 1
 
     backend be3
         log ${S3_addr}:${S3_port} daemon
         option log-health-checks
-        option mysql-check user user post-41
+        option mysql-check user user
         server srv ${h1_mysql2_addr}:${h1_mysql2_port} check inter 1s rise 1 fall 1
 
     backend be4