logging should support %doctest_mode

[quazgar]

There should be a way to log input and output in a doctest compatible way, so that the log can be used (maybe in a truncated form) for the standard doctest. Currently the only way I see is to switch to %doctest_mode, perform the commands as needed (maybe from a previous log file) and copy&paste the shell content to a new file.

Proposal:
Add a new option (maybe -d) to %logstart that saves the input and output accordingly.

I have ipython 0.10, used with python 2.6.4, on a 64bit Linux.

[Fernando Perez (fdo.perez)]

In trunk, '%hist -p' prints 'classic' prompts as well:

      -p: print classic '>>>' python prompts before each input. This is useful
       for making documentation, and in conjunction with -o, for producing
       doctest-ready output.