recall:  Fix stack crawl on 32-bit Linux

When called from main(), get_top_frame() returns a NULL value.  (There's
no stack crawl support for 64-bit Linux at all, so that's not an issue.)

Report the stack frame pointer as one level less deep into the stack (at
a lower memory address).  A stack frame whose address matches the bottom
(as sampled by calling get_stack_frame_pointer() in the main() function)
should now be included rather than omitted from a backtrace.
[NEW] utcp:  unet connector for TCP connections