pgsql: Move DTK_ISODOW DTK_DOW and DTK_DOY to be type UNITS rather than

Move DTK_ISODOW DTK_DOW and DTK_DOY to be type UNITS rather than
RESERV. RESERV is meant for tokens like "now" and having them in that
category throws errors like these when used as an input date:

stark=# SELECT 'doy'::timestamptz;
ERROR:  unexpected dtype 33 while parsing timestamptz "doy"
LINE 1: SELECT 'doy'::timestamptz;
               ^
stark=# SELECT 'dow'::timestamptz;
ERROR:  unexpected dtype 32 while parsing timestamptz "dow"
LINE 1: SELECT 'dow'::timestamptz;
               ^

Found by LLVM's Libfuzzer

Branch
------
REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/dd04d43bfda7d4475819822dc92fcecfd8627b7b

Modified Files
--------------
src/backend/utils/adt/datetime.c  |    6 +--
src/backend/utils/adt/timestamp.c |   80 ++++++++++++++++++-------------------
2 files changed, 43 insertions(+), 43 deletions(-)