Add a regression test to verify that the stack depth checker actually

works (and max_stack_depth is not set too high for the platform).
Inspired by trouble report from Brian Betts.

src/test/regress/expected/errors.out

@@ -441,3 +441,10 @@ NULL);
 ERROR:  syntax error at or near "NUL" at character 190
 LINE 16: ...L, id2 TEXT NOT NULL PRIMARY KEY, id3 INTEGER NOT NUL, id4 I...
                                                               ^
+-- Check that stack depth detection mechanism works and
+-- max_stack_depth is not set too high
+create function infinite_recurse() returns int as
+'select infinite_recurse()' language sql;
+\set VERBOSITY terse
+select infinite_recurse();
+ERROR:  stack depth limit exceeded

src/test/regress/sql/errors.sql

@@ -367,3 +367,10 @@ INT4
 UNIQUE 
 NOT 
 NULL);
+
+-- Check that stack depth detection mechanism works and
+-- max_stack_depth is not set too high
+create function infinite_recurse() returns int as
+'select infinite_recurse()' language sql;
+\set VERBOSITY terse
+select infinite_recurse();