enable checkpoint support

[Darío Suárez]

Hello,
I'm trying to use checkpoints under Linux debian unstable with debian 
kernel 2.6.15 and gdb 6.4-debian, but I always get undefined command 
when typing checkpoint. After downloading and compiling the gdb source 
code I get the same error. Could you give me any hints to turn on the 
feature, please? I have checked on Internet but I didn't find any useful 
information.

Cheers,
    Darío