Don't use the cvar ARCHIVE flag when writing to autogen.cfg.

In /listcvars output, use 'A' to indicate user-set (archived).
No longer use 'a'.
Make /<cvar> … equivalent to /seta <cvar> …
Remove variable setting flags and tidy up related help text.
Remove extra commands as voted.
Merge branch 'cvar-bits' into 'for-0.24'