Fix planning of star-schema-style queries.

 Fix planning of star-schema-style queries.
 
 Part of the intent of the parameterized-path mechanism was to handle
 star-schema queries efficiently, but some overly-restrictive search
 limiting logic added in commit e2fa76d80ba571d4de8992de6386536867250474
 prevented such cases from working as desired.  Fix that and add a
 regression test about it.  Per gripe from Marc Cousin.
 
 This is arguably a bug rather than a new feature, so back-patch to 9.2
 where parameterized paths were introduced.