disallow @ in table names

[sanikolaev]

Currently it's possible to create a table with a name starting with @

mysql> create table @f(f text);  
Query OK, 0 rows affected (0.01 sec)  

Let's disallow this, reserving the at sign for other purposes.

By the way, using @ anywhere but at the beginning of the table name already results in an error:

mysql> create table a@bc(a int);  
--------------  
create table a@bc(a int)  
--------------  
  
ERROR 1064 (42000): P03: syntax error, unexpected '(', expecting '=' near '(a int)'  

[githubmanticore]

➤ Sergey Nikolaev commented:

@smth can also break the integration with mysqldump:

➜  ~ mysqldump -P9306 -h0 Manticore > /tmp/dump.sql 
mysqldump: Couldn't execute 'show fields from `@a`': P01: syntax error, unexpected identifier, expecting VARIABLES near 'fields from `@a`' (1064) 

[sanikolaev]

Done in abf192a