mysql patch for a more flexible has_table() function

becuase show_table_status acts really weird, particularly on old versions, with unicode names, and external schemas, consider this patch which will just do a "DESCRIBE" and catch the error if table doesnt exist.

Index: lib/sqlalchemy/databases/mysql.py
===================================================================
--- lib/sqlalchemy/databases/mysql.py   (revision 2550)
+++ lib/sqlalchemy/databases/mysql.py   (working copy)
@@ -364,12 +364,25 @@

     def has_table(self, connection, table_name, schema=None):
         # TODO: this does not work for table names that contain multibyte characters.
-        # i have tried dozens of approaches here with no luck.  statements like
-        # DESCRIBE and SHOW CREATE TABLE work better, but they raise an error when
-        # the table does not exist.
-        cursor = connection.execute("show table status like %s", [table_name](table_name))
-        return bool( not not cursor.rowcount )

+        # http://dev.mysql.com/doc/refman/5.0/en/error-messages-server.html
+
+        # Error: 1146 SQLSTATE: 42S02 (ER_NO_SUCH_TABLE)
+        # Message: Table '%s.%s' doesn't exist
+
+        # Error: 1046 SQLSTATE: 3D000 (ER_NO_DB_ERROR)
+        # Message: No database selected
+
+        try:
+            name = schema and ("%s.%s" % (schema, table_name)) or table_name
+            connection.execute("DESCRIBE %s" % name)
+            return True
+        except exceptions.SQLError:
+            if e.orig.args[0](0) in (1146, 1046): 
+                return False
+            else:
+                raise
+
     def reflecttable(self, connection, table):
         # reference:  http://dev.mysql.com/doc/refman/5.0/en/name-case-sensitivity.html
         cs = connection.execute("show variables like 'lower_case_table_names'").fetchone()[1](1)
@@ -377,7 +390,7 @@
             cs = cs.tostring()
         case_sensitive = int(cs) == 0

-        decode_from = connection.execute("show variables like 'character_Set_results'").fetchone()[1](1)
+        decode_from = connection.execute("show variables like 'character_set_results'").fetchone()[1](1)

         if not case_sensitive:
             table.name = table.name.lower()

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