msg bufferisation (only)

I messed up the previous pull request by not being on a feature branch on my fork. This is now fixed. Please refer to the original pull-request here: https://github.com/longld/peda/pull/6

The buffering now handles nested calls well. That seemed to be the problem with the bug you described: peda help didn't work when gdb was started without a binary.

Please tell me if there are any other problems.