The grammar for a lambda context can include <source-name> 'M', and we
were adding the component that generated to the substitution table
twice.  Just ignore the 'M' completely -- we'll already have done the
checks we need when we saw its predecessor.  A prefix cannot be the
last component of a nested name, so we do not need to check for that
case (although we could if we wanted to be more lenient).

nathan

-- 
Nathan Sidwell