Add tests for strings and varchar.

 to NOTICE messages so that execution proceeds rather than halting.
 These clauses are ignored as stated in the messages.
Allow NOT NULL UNIQUE syntax (both were allowed individually before).
Allow Postgres-style casting ("::") of non-constants.

 No functional changes this time!

 btree support functions. Don't know why this was that way, but would
 assume that these should be consistant with all other types with
 hash support. Regression tests OK.
Change a few comments and field alignment to make things more readable.

 certainly OK for datetime since it is a float8 and should be OK for
 timespan since the first field within timespan is a float8.
Use float8 hash function for time type (rather than char8).

 since I've run ./duplicate_oids (and found no problems) in the last
 couple of months.
Add and modify some DESCR() entries to describe functions.

 Don't know why these few were not already this way, and don't know if
  there is some hidden problem with this, but assume it was done
  accidentally as entries were copied from other operators.
 Regression tests are OK, but...
Move one block of declaration source to keep OIDs in increasing order.
 Did not change OID values, just moved source code.

 Lost these when some include files were reorganized.
 Regression test could not compile.