Fix Boost version detection.

Issue #184.
Enable synonyms for deprecated functions.

Synonyms for deprecated Boost::Filesystem v2 functions such as
path::file_string() aren't enabled by default.  We'll turn on on for now
since we use them everywhere.

Issue #184.
Boost::Filesystem v3 doesn't have wide versions.

In Boost::Filesystem v3, there's only boost::filesystem::path, no wpath.
Although Boost provides a typedef for backwards compatibility, it's
actually making things harder to figure out, so we won't use it.

Issue #184.