API change: mysql_shutdown() now needs a 2nd parameter, the shutdown level.

Server will however still accept shutdown without specified level; so that old
mysqladmin can still shut server down.
I would like your comments on the names of shutdown level which I chose. You
are welcome to propose better names. Please however check WL#709 before.
Reason for the names I propose is to be accurate, thus leaving possibility
for other levels which we may imagine in the future; that's why I have rejected
names like "fast", "smart", "graceful" so far. My position is that WAIT_ALL_BUFFERS
or WAIT_CRITICAL_BUFFERS say what the shutdown does, whereas for "smart", "fast" you
need to remember what it does.
This should be pushed in 4.1.3 but only after your comments.

include/mysql_com.h

@@ -223,6 +223,26 @@ enum enum_field_types { MYSQL_TYPE_DECIMAL, MYSQL_TYPE_TINY,
 #define FIELD_TYPE_INTERVAL    MYSQL_TYPE_ENUM
 #define FIELD_TYPE_GEOMETRY    MYSQL_TYPE_GEOMETRY
 
+enum enum_shutdown_level {
+  /*
+    We want levels to be in growing order of gracefulness. So we leave room
+    for future intermediate levels. For now, escalating one level is += 10;
+    later if we insert new levels in between we will need a function
+    next_shutdown_level(level). Note that DEFAULT does not respect the
+    growing property.
+  */
+  SHUTDOWN_DEFAULT= 255, /* mapped to WAIT_ALL_BUFFERS for now */
+  /*
+    Here is the list in growing order (the next does the previous plus
+    something). WAIT_ALL_BUFFERS is what we have now. Others are "this MySQL
+    server does not support this shutdown level yet".
+  */
+  SHUTDOWN_WAIT_CRITICAL_BUFFERS= 10, /* flush MyISAM buffs (no corruption) */
+  SHUTDOWN_WAIT_ALL_BUFFERS= 20, /* flush InnoDB buffers */
+  SHUTDOWN_WAIT_TRANSACTIONS= 30, /* wait for existing trans to finish */
+  SHUTDOWN_WAIT_CONNECTIONS= 40 /* wait for existing connections to finish */
+};
+
 /* options for mysql_set_option */
 enum enum_mysql_set_option
 {