pgsql: Create a quick-and-dirty list of known migration issues for

Log Message:
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Create a quick-and-dirty list of known migration issues for pre-8.3
users of tsearch.  This isn't meant to be permanent documentation,
but to call out the areas that need either fixing or real documentation.

Modified Files:
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    pgsql/doc/src/sgml:
        textsearch.sgml (r1.21 -> r1.22)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/textsearch.sgml?r1=1.21&r2=1.22)