python module dependencies

[volca02]

...as was reported - the python module dependency on .so is vague (in the deb depends) leading to possible discrepancies in the symbol exports/imports.

Resulting situation was as follows:

ImportError: /usr/lib/python3/dist-packages/_fastrpc.cpython-35m-x86_64-linux-gnu.so: undefined symbol: _ZN4FRPC8HTTPIO_t15waitOnReadyReadEv

Having an equals sign for exact dependency based on version (i.e. depends libfastrpc8 (=8.X.Y)) could be beneficial for the stability of the project.