A number of small changes. Mainly they are to pacify
'checkdoc-ispell' (if it seems appropriate) and to standardise the
names of the packages you can link to from within Org-mode. I am
using the package names as spelt or abbreviated in their own
documentation (if I have been able to find it easily). Thus, for
example, prefer MH-E over MHE, Rmail over RMAIL etc.
This files are stil all loaded automatically, but the user can turn
individual files off. Also, this makes maintaining the link
stuff easier, because everything related to a specific link type
is in one place.