Stop setting etype in the MD crypto code. So far we have set the etype

Stop setting etype in the MD crypto code.  So far we have set the etype
and returned the error, which made the MI crypto code set the etype for
a second time.  We still have to set etype after calling the MD process
function, as the callers of crypto_invoke() still expect error handling
to be shown through the etype.  But at least now all MD crypto code does
not have to worry about that anymore.  Once the callers are changed to
not look at etype anymore, we can get rid of it completely.

ok tobhe@