pgsql: Allow leading and trailing whitespace in the input to the boolean

Log Message:
-----------
Allow leading and trailing whitespace in the input to the boolean
type. Also, add explicit casts between boolean and text/varchar. Both
of these changes are for conformance with SQL:2003.

Update the regression tests, bump the catversion.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        datatype.sgml (r1.202 -> r1.203)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/datatype.sgml.diff?r1=1.202&r2=1.203)
    pgsql/src/backend/utils/adt:
        bool.c (r1.38 -> r1.39)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/bool.c.diff?r1=1.38&r2=1.39)
    pgsql/src/include/catalog:
        catversion.h (r1.408 -> r1.409)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h.diff?r1=1.408&r2=1.409)
        pg_cast.h (r1.32 -> r1.33)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_cast.h.diff?r1=1.32&r2=1.33)
        pg_proc.h (r1.456 -> r1.457)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h.diff?r1=1.456&r2=1.457)
    pgsql/src/include/utils:
        builtins.h (r1.293 -> r1.294)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/builtins.h.diff?r1=1.293&r2=1.294)
    pgsql/src/test/regress/expected:
        boolean.out (r1.12 -> r1.13)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/boolean.out.diff?r1=1.12&r2=1.13)
    pgsql/src/test/regress/sql:
        boolean.sql (r1.7 -> r1.8)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/boolean.sql.diff?r1=1.7&r2=1.8)