pgsql: Create a standard function pg_sleep() to sleep for a specified

Log Message:
-----------
Create a standard function pg_sleep() to sleep for a specified amount of time.
Replace the former ad-hoc implementation used in the regression tests.
Joachim Wieland

Modified Files:
--------------
    pgsql/doc/src/sgml:
        func.sgml (r1.301 -> r1.302)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/func.sgml.diff?r1=1.301&r2=1.302)
    pgsql/src/backend/utils/adt:
        misc.c (r1.49 -> r1.50)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/misc.c.diff?r1=1.49&r2=1.50)
    pgsql/src/include/catalog:
        catversion.h (r1.309 -> r1.310)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/catversion.h.diff?r1=1.309&r2=1.310)
        pg_proc.h (r1.390 -> r1.391)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/catalog/pg_proc.h.diff?r1=1.390&r2=1.391)
    pgsql/src/include/utils:
        builtins.h (r1.269 -> r1.270)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/builtins.h.diff?r1=1.269&r2=1.270)
    pgsql/src/test/regress/expected:
        stats.out (r1.6 -> r1.7)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/expected/stats.out.diff?r1=1.6&r2=1.7)
    pgsql/src/test/regress/input:
        create_function_1.source (r1.15 -> r1.16)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/input/create_function_1.source.diff?r1=1.15&r2=1.16)
    pgsql/src/test/regress/output:
        create_function_1.source (r1.26 -> r1.27)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/output/create_function_1.source.diff?r1=1.26&r2=1.27)
    pgsql/src/test/regress:
        regress.c (r1.64 -> r1.65)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/regress.c.diff?r1=1.64&r2=1.65)
    pgsql/src/test/regress/sql:
        stats.sql (r1.4 -> r1.5)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/sql/stats.sql.diff?r1=1.4&r2=1.5)