pgsql: Improve test coverage of CLOBBER_CACHE_ALWAYS by having it also

Log Message:
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Improve test coverage of CLOBBER_CACHE_ALWAYS by having it also force
reloading of operator class information on each use of LookupOpclassInfo.
Had this been in place a year ago, it would have helped me find a bug
in the then-new 'operator family' code.  Now that we have a build farm
member testing CLOBBER_CACHE_ALWAYS on a regular basis, it seems worth
expending a little bit of effort here.

Modified Files:
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    pgsql/src/backend/utils/cache:
        relcache.c (r1.264 -> r1.265)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/cache/relcache.c?r1=1.264&r2=1.265)