[patch] New test for set backtrace related functionality

[Andrew Cagney]

> Here's the tough problem.  I'm getting a weird random timeout on the
> "partial backtrace (using limit)" test.  In a group of 12
> configurations, I saw 2 PASS and 12 FAIL/timeout.  I suspect some ".*"
> or "[^foo]*" that is too greedy and eating more than it should, leaving
> the later bits of the expect_list out to dry.  gdb_expect_list is
> matching them one at a time so there is no backtracking if an early r.e.
> mistakenly eats too much.  Specifically, it might be a problem with the
> definition of $leadin.

Paul, were you able to reproduce this problem?

Andrew