In other words, cut out poliqarp from build if this flag is False.
The flag remains forced to be True by default, though.
This is mostly to be able to cut poliqarp out of pure WIN32 build until
such time it actually builds (it doesn't atm).

Plugin infrastructure in corpus2 readers: plugin loading code in pwrnlp/plugin, chanegs all around to accomodate

rename .i files in swig wrappers, correct dependendcies so touching any .i file will rebuild the wrappers

(swig) Added corpus2 library. To use corpus2 python library (wrappers for C++ corpus2) you should do: 'import corpus2' in python