Improve context display for failures during COPY IN, as recently

discussed on pghackers.

src/test/regress/expected/alter_table.out

@@ -998,7 +998,7 @@ copy test("........pg.dropped.1........") to stdout;
 ERROR:  column "........pg.dropped.1........" of relation "test" does not exist
 copy test from stdin;
 ERROR:  extra data after last expected column
-CONTEXT:  COPY FROM, line 1
+CONTEXT:  COPY test, line 1: "10	11	12"
 select * from test;
  b | c 
 ---+---

src/test/regress/expected/copy2.out

@@ -35,17 +35,17 @@ ERROR:  column "d" specified more than once
 -- missing data: should fail
 COPY x from stdin;
 ERROR:  invalid input syntax for integer: ""
-CONTEXT:  COPY FROM, line 1
+CONTEXT:  COPY x, line 1, column a: ""
 COPY x from stdin;
 ERROR:  missing data for column "e"
-CONTEXT:  COPY FROM, line 1
+CONTEXT:  COPY x, line 1: "2000	230	23	23"
 COPY x from stdin;
 ERROR:  missing data for column "e"
-CONTEXT:  COPY FROM, line 1
+CONTEXT:  COPY x, line 1: "2001	231	\N	\N"
 -- extra data: should fail
 COPY x from stdin;
 ERROR:  extra data after last expected column
-CONTEXT:  COPY FROM, line 1
+CONTEXT:  COPY x, line 1: "2002	232	40	50	60	70	80"
 -- various COPY options: delimiters, oids, NULL string
 COPY x (b, c, d, e) from stdin with oids delimiter ',' null 'x';
 -- check results of copy in

src/test/regress/expected/domain.out

@@ -40,7 +40,7 @@ INSERT INTO basictest values ('88', 'haha', 'short', '123.1212');    -- Truncate
 -- Test copy
 COPY basictest (testvarchar) FROM stdin; -- fail
 ERROR:  value too long for type character varying(5)
-CONTEXT:  COPY FROM, line 1
+CONTEXT:  COPY basictest, line 1: "notsoshorttext"
 COPY basictest (testvarchar) FROM stdin;
 select * from basictest;
  testint4 | testtext | testvarchar | testnumeric 
@@ -127,11 +127,11 @@ INSERT INTO nulltest values ('a', 'b', 'c', NULL, 'd'); -- Good
 -- Test copy
 COPY nulltest FROM stdin; --fail
 ERROR:  domain dcheck does not allow null values
-CONTEXT:  COPY FROM, line 1
+CONTEXT:  COPY nulltest, line 1: "a	b	\N	d	\N"
 -- Last row is bad
 COPY nulltest FROM stdin;
 ERROR:  new row for relation "nulltest" violates check constraint "nulltest_col5"
-CONTEXT:  COPY FROM, line 3
+CONTEXT:  COPY nulltest, line 3: "a	b	c	\N	a"
 select * from nulltest;
  col1 | col2 | col3 | col4 | col5 
 ------+------+------+------+------

src/test/regress/output/constraints.source

@@ -274,7 +274,7 @@ SELECT '' AS two, * FROM COPY_TBL;
 
 COPY COPY_TBL FROM '@abs_srcdir@/data/constrf.data';
 ERROR:  new row for relation "copy_tbl" violates check constraint "copy_con"
-CONTEXT:  COPY FROM, line 2
+CONTEXT:  COPY copy_tbl, line 2: "7	check failed	6"
 SELECT * FROM COPY_TBL;
  x |       y       | z 
 ---+---------------+---