Parser rejects valid INTERVAL() expressions when associated with
arithmetic operators. The problem is the way in which the expression
and interval grammar rules were organized caused shift/reduce conflicts.

The solution is to tweak the interval rules to avoid shift/reduce
conflicts by removing the broken interval_expr rule and explicitly
specify it's content where necessary.

Original fix by Davi Arnaut, revised and improved rules by Marc Alff


mysql-test/r/parser.result:
  Add test case result for Bug#22312
mysql-test/t/parser.test:
  Add test case for Bug#22312
sql/sql_yacc.yy:
  Resolve shift/reduce conflicts by reorganizing the interval
  expression rules.