Favor linking against non-versioned shared object.

[qdii]

Suppose that /usr/lib has:

libboost_regex.so -> libboost_regex.so.1.55.0
libboost_regex.so.1.55.0

BOOST_REGEX will set BOOST_REGEX_LIBS to libboost_regex.so.1.55.0, which in turns creates a dependency from the binary to a very specific version of boost.

BOOST_REGEX_LIBS should be set to libboost_regex.so so that the binary can be used with different versions of boost. It is the package maintainer's job to ensure that the system's runtime loads one of the correct version of boost.