sendmail wording change

[Jeff Johnson]

FHS version 2.3, /usr/lib section:

Specific Options

For historical reasons, /usr/lib/sendmail must be a
symbolic link to /usr/sbin/sendmail if the latter exists. [24]

However, I'm observing that current Linux distros do not implement in this way.
 For example, it's quite common for /usr/sbin/semdail and /usr/lib/sendmail
both to be symlinks off somewhere else, for example an /etc/alternatives
directory entry which ultimately resolves to the real MTA. However, they *are*
providing a /usr/lib/sendmail symlink which *does* resolve to the actual MTA.
The replacement wording should permit /usr/lib/sendmail to be a symbolic link
which resolves to the system's MTA of choice without requiring that it point
specifically to /usr/sbin/sendmail.

The following examples show three different implementions where both names
exist, and end up resolving to the same executable, but none follow the current
FHS guideline to the letter.

Observed example 1:
/usr/lib/sendmail -> /etc/alternatives/mta-in_libdir
/usr/sbin/sendmail -> /etc/alternatives/mta
/etc/alternatives/mta-in_libdir -> /usr/sbin/sendmail.postfix
/etc/alternatives/mta -> /usr/sbin/sendmail.postfix

Observed example 2:
/usr/lib/sendmail -> /etc/alternatives/mta-sendmail
/usr/sbin/sendmail -> /etc/alternatives/mta
/etc/alternatives/mta-sendmail -> /usr/lib/sendmail.sendmail
/etc/alternatives/mta -> /usr/sbin/sendmail.sendmail
/usr/lib/sendmail.sendmail -> /usr/sbin/sendmail.sendmail

Observed example 3:
/usr/lib/sendmail -> /usr/sbin/exim
/usr/sbin/sendmail -> exim