Fix assorted compilation failures in contrib

Evidently I failed to test a compile after my earlier header shuffling.

contrib/auto_explain/auto_explain.c

@@ -12,6 +12,8 @@
  */
 #include "postgres.h"
 
+#include <limits.h>
+
 #include "commands/explain.h"
 #include "executor/instrument.h"
 #include "utils/guc.h"

contrib/dblink/dblink.c

@@ -41,6 +41,7 @@
 #include "catalog/pg_type.h"
 #include "executor/spi.h"
 #include "foreign/foreign.h"
+#include "lib/stringinfo.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
 #include "parser/scansup.h"

contrib/pageinspect/fsmfuncs.c

@@ -18,10 +18,12 @@
  */
 
 #include "postgres.h"
+
+#include "funcapi.h"
+#include "lib/stringinfo.h"
+#include "miscadmin.h"
 #include "storage/fsm_internals.h"
 #include "utils/builtins.h"
-#include "miscadmin.h"
-#include "funcapi.h"
 
 Datum		fsm_page_contents(PG_FUNCTION_ARGS);
 

contrib/tablefunc/tablefunc.c

@@ -35,8 +35,9 @@
 #include <math.h>
 
 #include "catalog/pg_type.h"
-#include "funcapi.h"
 #include "executor/spi.h"
+#include "funcapi.h"
+#include "lib/stringinfo.h"
 #include "miscadmin.h"
 #include "utils/builtins.h"