Hello,

This patch enables the `is the prev frame identical to this frame' check 
in get_prev_frame().  I forgot to enable it when I switched the frame ID 
code from using the frame's PC to using the frame's function.  Noticed 
this when reviewing Daniel's Arm frame update.

It should probably go straight into the mainline (tested on i386 and d10v).

Thoughts on 6?

Andrew