Let torsocks run from source directory

I don't know how complicated it is to implement, it can be handy to run torsocks from source to test patches.

src/bin/torsocks is not executable and before running 'make install' it returns:

$ sh src/bin/torsocks --version
ERROR: /usr/local/lib/torsocks/libtorsocks.so does not exist! Try re-installing torsocks.