Properly rebuild SYS_COLUMNS metadata

innobase_add_one_virtual(), innobase_insert_sys_virtual(): Change
the return type to bool, and invoke my_error() when detecting an error.

innodb_insert_sys_columns(): Insert a record into SYS_COLUMNS.
Refactored from innobase_add_one_virtual() and innobase_instant_add_col().

innobase_instant_add_col(): Replace the parameter dfield with type.

innobase_instant_drop_cols(): Drop matching columns from SYS_COLUMNS
and all columns from SYS_VIRTUAL.

innobase_instant_try(): Only invoke innobase_instant_drop_cols() when
there are other changes than adding columns last.

innodb_update_cols(): Renamed from innodb_update_n_cols().

storage/innobase/row/row0mysql.cc

@@ -330,6 +330,7 @@ row_mysql_read_geometry(
 	ulint		col_len)	/*!< in: MySQL format length */
 {
 	byte*		data;
+	ut_ad(col_len > 8);
 
 	*len = mach_read_from_n_little_endian(ref, col_len - 8);