Fix psql's counting of script file line numbers during COPY.

handleCopyIn incremented pset.lineno for each line of COPY data read from
a file.  This is correct when reading from the current script file (i.e.,
we are doing COPY FROM STDIN followed by in-line data), but it's wrong if
the data is coming from some other file.  Per bug #6083 from Steve Haslam.
Back-patch to all supported versions.

src/bin/psql/copy.c

@@ -841,7 +841,8 @@ handleCopyIn(PGconn *conn, FILE *copystream, bool isbinary)
 				}
 			}
 
-			pset.lineno++;
+			if (copystream == pset.cur_cmd_source)
+				pset.lineno++;
 		}
 	}