Fix some bogus direct uses of realloc().

pg_dump/parallel.c was using realloc() directly with no error check.
While the odds of an actual failure here seem pretty low, Coverity
complains about it, so fix by using pg_realloc() instead.

While looking for other instances, I noticed a couple of places in
psql that hadn't gotten the memo about the availability of pg_realloc.
These aren't bugs, since they did have error checks, but verbosely
inconsistent code is not a good thing.

Back-patch as far as 9.3.  9.2 did not have pg_dump/parallel.c, nor
did it have pg_realloc available in all frontend code.

src/bin/pg_dump/parallel.c

@@ -1308,7 +1308,7 @@ readMessageFromPipe(int fd)
 		{
 			/* could be any number */
 			bufsize += 16;
-			msg = (char *) realloc(msg, bufsize);
+			msg = (char *) pg_realloc(msg, bufsize);
 		}
 	}
 
@@ -1316,7 +1316,7 @@ readMessageFromPipe(int fd)
 	 * Worker has closed the connection, make sure to clean up before return
 	 * since we are not returning msg (but did allocate it).
 	 */
-	free(msg);
+	pg_free(msg);
 
 	return NULL;
 }