per thread breakpoints

[Quality Quorum]

Hi, 

It seems to me that gdb core does NOT seriously support per thread breaks:

1. target_insert_breakpoint() is unaware about thread associated with
   a breakpoint.

2. insert_breakpoints() does not do any dances with inferior pids before 
   and after calls to target_insert_breakpoint().

I would suppose it should be fixed ASAP (e.g. by adding pid argument to 
to the target_insert_breakpoint): it is a huge resource hog in 
case of remote debugging and it seems like linux threads would also
greatly benefit from this improvement.

Thanks,

Aleksey