replace the remaining occurences of sed with emacs scripts, implement mkdir with...

replace the remaining occurences of sed with emacs scripts, implement mkdir with install

* UTILITIES/org-fixup.el (org-make-local-mk): New function to create a
  local.mk template from default.mk.

* UTILITIES/org-fixup.el (org-make-letterformat): New function to
  replace the format string for A4 with one for Letter.

* default.mk: Few cosmetic changes to the template section.  Add
  definition MAKE_LOCAL_MK for call to org-make-local-mk.  Remove
  definition for SED, which is not used anymore.  Implement MKDIR with
  'install -d' by default.  Since both CP and MKDIR are now
  implemented with install, this reduces the number of external
  dependencies.  Add mode settings to both invocations of install to
  keep the modes of installed files sane even if umask is set to a
  strange value.

* targets.mk: Remove sed script and use $(MAKE_LOCAL_MK) instead.

* doc/Makefile: Remove sed script and replace with emacs script.  This
  script can not be placed into a variable since it would expand $<
  and $@ in the context of the "card" target rather than the pattern
  rule.