The problem was that in the first production in rule 'join_table', that
processes simple cross joins, the parser was processing the second join operand
before the first one due to unspecified priorities of JOINs. As a result in the
case of cross joins the parser constructed a tree with incorrect nesting:
the expression "t1 join t2 join t3 on some_cond" was interpreted as
"t1 join (t2 join t3 on some_cond)" instead of
"(t1 join t2) join t3 on some_cond".
Because of this incorrect nesting the method make_join_on_context picked an
incorrect table as the first table of the name resolution context.

The solution assignes correct priorities to the related production.


mysql-test/r/select.result:
  Added test for BUG#12943.
mysql-test/t/select.test:
  Added test for BUG#12943.
sql/sql_parse.cc:
  Fixed typo.
sql/sql_yacc.yy:
  Provide explicit priorities of the JOIN operator and the 'table_ref' rule,
  to enforce left-associativity of [INNER | CROSS] JOIN.