Check for interrupts and stack overflow during rule/view dumps.

Since ruleutils.c recurses, it could be driven to stack overflow by
deeply nested constructs.  Very large queries might also take long
enough to deparse that a check for interrupts seems like a good idea.
Stick appropriate tests into a couple of key places.

Noted by Greg Stark.  Back-patch to all supported branches.

src/backend/utils/adt/ruleutils.c

@@ -37,6 +37,7 @@
 #include "commands/tablespace.h"
 #include "executor/spi.h"
 #include "funcapi.h"
+#include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
 #include "optimizer/tlist.h"
@@ -4133,6 +4134,10 @@ get_query_def(Query *query, StringInfo buf, List *parentnamespace,
 	deparse_context context;
 	deparse_namespace dpns;
 
+	/* Guard against excessively long or deeply-nested queries */
+	CHECK_FOR_INTERRUPTS();
+	check_stack_depth();
+
 	/*
 	 * Before we begin to examine the query, acquire locks on referenced
 	 * relations, and fix up deleted columns in JOIN RTEs.	This ensures
@@ -4689,6 +4694,10 @@ get_setop_query(Node *setOp, Query *query, deparse_context *context,
 	StringInfo	buf = context->buf;
 	bool		need_paren;
 
+	/* Guard against excessively long or deeply-nested queries */
+	CHECK_FOR_INTERRUPTS();
+	check_stack_depth();
+
 	if (IsA(setOp, RangeTblRef))
 	{
 		RangeTblRef *rtr = (RangeTblRef *) setOp;
@@ -6526,6 +6535,10 @@ get_rule_expr(Node *node, deparse_context *context,
 	if (node == NULL)
 		return;
 
+	/* Guard against excessively long or deeply-nested queries */
+	CHECK_FOR_INTERRUPTS();
+	check_stack_depth();
+
 	/*
 	 * Each level of get_rule_expr must emit an indivisible term
 	 * (parenthesized if necessary) to ensure result is reparsed into the same