Pending breakpoint id change

[Vladimir Prus]

Is there any reason why when a pending breakpoint is resolved, instead of reusing
the same breakpoint id, a new breakpoint is created?

This behaviour might be fine for CLI, but for MI frontend it really confuses thing
since there's no MI notification that pending breakpoint N was resolved into breakpoint
M. Such notification could be added, of course, but preventing gdb from creating
new breakpoint would be a more straight-forward approach.

- Volodya