error out in a bit more friendly way when the user is trying to use
config(1) on a too old or too recent source tree.
To achieve that, introduce the "version NUMBER" statement which can be use
about anywhere in the config files. Also, use two defines, CONFIG_VERSION
(which is the actual version of binary), and CONFIG_MINVERSION, which is
the minimum version the binary supports.
Allowing a range of versions serves several purposes: first it allows me
to introduce the versioning without requiring it to be used right away in
the kernel tree, which means it will be possible to introduce new features
of config(1) rather progressively in the future. E.g., using 'no pci' in
a config file could only require the new version in that config file, so
that the rest remains compatible.
In the end, an actual bump of the main config system (i.e., in conf/files)
will only be required when e.g., ioconf.c semantics change.
(Mostly-)silently accepted on tech-kern. Error messages turned into
correct and meaningful English thanks to Tracy and Perry.
437f8925a6