http://www.postfix.org/DATABASE_README.html#types specifies the lookup
table types postfix understands.
Most are defined as type:/path/to/table which is currently supported
by the postfix formula.
This does break though as soon as the proxy table type is used which is
a prefix to a normal table definition to indicate caching is requested.
This PR changes the code to discard the proxy prefix to ensure that the
usual logic applies again.
9281c79aec