The image activator checks to see if the space for the path of the interpreter
is larger then MAXPATHLEN. This is bad since it should check the length
of the interpreter is less then MAXPATHLEN. Update the error message to
give a better idea of why a binary won't run.
Also on failure, only free interp_buf if it is not NULL to prevent double
free. Do the VOP_UNLOCK even if it is not locked. I'm not sure about
this but the success part does this so I'm following suite.