PL/Tcl: Improve trigger tests organization

The trigger tests for PL/Tcl were spread aroud pltcl_setup.sql and
pltcl_queries.sql, mixed with other tests, which makes them hard to
follow and edit.  Move all the trigger-related pieces to a new file
pltcl_trigger.sql.  This also makes the test setup more similar to
plperl and plpython.

Author: petere

src/pl/tcl/Makefile

@@ -28,7 +28,7 @@ DATA = pltcl.control pltcl--1.0.sql pltcl--unpackaged--1.0.sql \
        pltclu.control pltclu--1.0.sql pltclu--unpackaged--1.0.sql
 
 REGRESS_OPTS = --dbname=$(PL_TESTDB) --load-extension=pltcl
-REGRESS = pltcl_setup pltcl_queries pltcl_call pltcl_start_proc pltcl_subxact pltcl_unicode pltcl_transaction
+REGRESS = pltcl_setup pltcl_queries pltcl_trigger pltcl_call pltcl_start_proc pltcl_subxact pltcl_unicode pltcl_transaction
 
 # Tcl on win32 ships with import libraries only for Microsoft Visual C++,
 # which are not compatible with mingw gcc. Therefore we need to build a