mysql dialect does not pass literal_binds to CAST

[Mike Bayer]

from sqlalchemy import cast, column, Integer

expr = cast(column('foo', Integer) + 5, Integer())

from sqlalchemy.dialects import mysql

print expr.compile(dialect=mysql.dialect(), compile_kwargs={"literal_binds": True})

output:

CAST(foo + %s AS SIGNED INTEGER)

[Mike Bayer]

Propagate kwargs to all MySQL CAST paths

Change-Id: I23a6abb26bbbe3d118887d043ce761fc4572d8d2 Fixes: #3766

→ <<cset af6f4ab938f1>>