Hello,

This patch adds a successor to "struct trad_frame_saved_reg" - "struct 
trad_frame_cache".  Unlike the former, the latter:

- has space for a frame ID and ABI base
- is opaque

For the moment I've included a minimal set of methods), more will 
follow.  My signal trampoline code uses this as a common template for 
describing the location of registers saved in a signal trampoline.

Comments?  I'll look to commit in a few days,
Andrew