Notes on the handling of /etc/voyage.conf

The distribution file {dist}/etc/voyage.conf will contain default values for
the key configuration environment variables.  These variables will include
VOYAGE_PROFILE (which specifies the basic profile being used for the target
system), and such things as VOYAGE_SYSTEM_CONSOLE (whether the control terminal
is "console" [vga] or "serial"), VOYAGE_SYSTEM_SERIAL (the async speed to use
on serial console), VOYAGE_SYSTEM_PCMCIA (whether the system supports pcmcia),
and so forth.

Besides the "profile-related" variables, there will also be "system-related"
variables such as VOYAGE_SYSTEM_SYNCDIRS (a list of directories which need to
be copied from /ro to /rw during target system startup).

The voyage-install.sh script will read this file from the distribution
directory and set the environment variables specified in it.  It will also
create a list of all the variable names, which will later control what will be
written out to the target system's voyage.conf file.  Later, whenever the user
changes the "profile" to be used, the script will read the requested
{dist}/etc/voyage-profile/{profile-name}.pro file and re-set the variables
appropriately.  If the profile contains any variables which were not in the
distribution's voyage.conf file, those variables will be added to the script's
internal list so that they will be included in the target's voyage.conf file.