gr-osmosdr fixes for soapy support, and msvc

Hey list, It looks like due to some GRC changes, the throw in set_iq_balance_mode() is no longer caught. Its causing a problem for GRC users and I would like upstream the fix. See soapy_support: http://cgit.osmocom.org/gr-osmosdr/log/?h=soapy_support I am building GNURadio and gr-osmosdr as part of my PothosSDR installer: https://github.com/pothosware/PothosSDR/wiki/GNURadio There were a few minor fixes to make for the MSVC compiler. The commits have explanatory messages, and I made sure that they were non-breaking. I would also like to upstream these fixes as well. See msvc_fixes: http://cgit.osmocom.org/gr-osmosdr/log/?h=msvc_fixes Thanks for your consideration, -josh