flush buffers, and options for livemap and msig

Just a few small improvements, if you want them:

- fflush(): to avoid a 4k buffering issue where the map file was always missing the most recent entries.
- livemap: an option to write to an alternate file. This allows other software to be used to tidy up and write the real map file before running perf. (This is a step I've found to be necessary with complex production code, where -- despite a correct map file and perf profile -- perf's translation step gets messed up, unless the map file is tidied first. I have a program to do this I'll publish.)
- msig: I changed the behavior to not include the method signatures, unless you set this option.

I also have a fix (or rather, a hack) in-hand for the frame pointer issue I need to publish as well...