Booのdllサーチパス追加

Booでimportするdllのサーチパスの追加は環境変数MONO_PATHで行うことができる。
下記man monoからの引用

MONO_PATH
       Provides a search path to the runtime where to look for library
       files.   This is a tool convenient for debugging applications, but
       should not be used by deployed applications as it breaks the assembly
       loader in subtle ways.
       Directories are separated by the platform path separator (colons on unix). Example:
       /home/username/lib:/usr/local/mono/lib
       Alternative solutions to MONO_PATH include: installing libraries into
       the Global Assembly Cache (see gacutil(1)) or having the dependent
       libraries side-by-side with the main executable.
       For a complete description of recommended practices for application
       deployment, see
       http://www.mono-project.com/Guidelines:Application_Deployment

LinuxなどではLD_LIBRARY_PATH同様':'区切りで列挙すればいい様子。