backtrace_on_internal_error

We have backtrace support for server errors.  You can activate that 
either by setting backtrace_functions or by explicitly attaching 
errbacktrace() to an ereport() call.

I would like an additional mode that essentially triggers a backtrace 
anytime elog() (for internal errors) is called.  This is not well 
covered by backtrace_functions, because there are many equally-worded 
low-level errors in many functions.  And if you find out where the error 
is, then you need to manually rewrite the elog() to ereport() to attach 
the errbacktrace(), which is annoying.  Having a backtrace automatically 
on every elog() call would be very helpful during development for 
various kinds of common errors from palloc, syscache, node support, etc.

I think the implementation would be very simple, something like

diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c
index 6aeb855e49..45d40abe92 100644
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -498,9 +498,11 @@ errfinish(const char *filename, int lineno, const 
char *funcname)

     /* Collect backtrace, if enabled and we didn't already */
     if (!edata->backtrace &&
-       edata->funcname &&
-       backtrace_functions &&
-       matches_backtrace_functions(edata->funcname))
+       ((edata->funcname &&
+         backtrace_functions &&
+         matches_backtrace_functions(edata->funcname)) ||
+        (edata->sqlerrcode == ERRCODE_INTERNAL_ERROR &&
+         backtrace_on_internal_error)))
         set_backtrace(edata, 2);

     /*

where backtrace_on_internal_error would be a GUC variable.

Would others find this useful?  Any other settings or variants in this 
area that should be considered while we're here?