MEDIUM: vars: pre-create parsed SCOPE_PROC variables as permanent ones

MEDIUM: vars: pre-create parsed SCOPE_PROC variables as permanent ones

All variables whose names are parsed by the config parser, the
command-line parser or the SPOE's register-var-names parser are
now preset as permanent. This will guarantee that these variables
will exist through out all the process' life, and that it will be
possible to implement the "ifexist" feature by looking them up.

This was marked medium because pre-setting a variable with an empty
value may always have side effects, even though none was spotted at
this stage.