use location of OpenTap.dll instead of entry assembly
Use the environment set by tap.exe instead of the executing assembly (which was tap.exe, or something else in the same directory in almost all cases)
If this value is not available (when OpenTap is loaded by external programs instead of tap.exe), use the location of OpenTap.dll.
Closes #606 (closed)
Edited by Alexander Nørskov Larsen