Remove unneeded typedef

docstring is already defined in strfwd.h (which is included from docstring.h).
There are only two possible cases:
Either the typedef in docstring.h defines an identical type (then it is not
needed), or it defines a different type (then it generates a compilation error)
=> it is not needed.
Merge remote-tracking branch 'github/build-bot-master' into bleeding-edge-master
2014.12.03-21.00