Fix edebug specs.
Fix docstring.
install.el (install-prefix): Handle new installing method on MS-Windows.
install.el (install-prefix): Minor refactoring.
Prefer iso-8859-15 to iso-8859-6 and so on.
mcs-e20.el (coding-system-to-mime-charset): Exclude non-standard charset from result.
Merge remote-tracking branch 'ikazuhiro/master' into apel-wl
Make detect-mime-charset-region slightly less horrible.

In order to detect the right charset to use for a text part, we used
to convert the region to a string, then convert that string to a list,
then uniquify the resulting list.  We now build the unique list on the
fly.