Some more gitignore cleanups: cover contrib and PL regression test outputs.

Also do some further work in the back branches, where quite a bit wasn't
covered by Magnus' original back-patch.

contrib/btree_gin/.gitignore

 /btree_gin.sql
+# Generated subdirectories
+/results/

contrib/btree_gist/.gitignore

 /btree_gist.sql
+# Generated subdirectories
+/results/

contrib/citext/.gitignore

 /citext.sql
+# Generated subdirectories
+/results/

contrib/cube/.gitignore

 /cubeparse.c
 /cubescan.c
 /cube.sql
+# Generated subdirectories
+/results/

contrib/dblink/.gitignore

 /dblink.sql
+# Generated subdirectories
+/results/

contrib/dict_int/.gitignore

 /dict_int.sql
+# Generated subdirectories
+/results/

contrib/dict_xsyn/.gitignore

 /dict_xsyn.sql
+# Generated subdirectories
+/results/

contrib/earthdistance/.gitignore

 /earthdistance.sql
+# Generated subdirectories
+/results/

contrib/hstore/.gitignore

 /hstore.sql
+# Generated subdirectories
+/results/

contrib/intarray/.gitignore

 /_int.sql
+# Generated subdirectories
+/results/

contrib/ltree/.gitignore

 /ltree.sql
+# Generated subdirectories
+/results/

contrib/pg_trgm/.gitignore

 /pg_trgm.sql
+# Generated subdirectories
+/results/

contrib/pgcrypto/.gitignore

 /pgcrypto.sql
+# Generated subdirectories
+/results/

contrib/seg/.gitignore

 /segparse.c
 /segscan.c
 /seg.sql
+# Generated subdirectories
+/results/

contrib/tablefunc/.gitignore

 /tablefunc.sql
+# Generated subdirectories
+/results/

contrib/test_parser/.gitignore

 /test_parser.sql
+# Generated subdirectories
+/results/

contrib/tsearch2/.gitignore

 /tsearch2.sql
+# Generated subdirectories
+/results/

contrib/unaccent/.gitignore

 /unaccent.sql
+# Generated subdirectories
+/results/

contrib/xml2/.gitignore

+# Generated subdirectories
+/results/

src/pl/plperl/.gitignore

@@ -2,3 +2,6 @@
 /Util.c
 /perlchunks.h
 /plperl_opmask.h
+
+# Generated subdirectories
+/results/

src/pl/plpython/.gitignore

+# Generated subdirectories
+/results/

src/pl/tcl/.gitignore

+# Generated subdirectories
+/results/

src/pl/tcl/modules/.gitignore

+/pltcl_delmod
+/pltcl_listmod
+/pltcl_loadmod