Pure virtual classes should declare pure virtual member functions as 0, rather...

Pure virtual classes should declare pure virtual member functions as 0, rather than having the linker go looking for implementations elesewhere.  This lets the compiler generate better error messages when a subclass fails to implement one or more required functions.


git-svn-id: https://arducopter.googlecode.com/svn/trunk@1339 f9c3cf11-9bcb-44bc-f272-b75c42450872