A variable name is stored internally with its section the way it
appeared in the configuration file in order to have the information
about what parts are case-sensitive inline.

Really implement parse_section_header_ext and move the assignment of
variables to config_parse.

The variable name matching is now done in a case-away way by
cvar_name_match and cvar_section_match. Before the user sees it, it's
normalized to the two- or three-dot version.

Signed-off-by: Carlos Martín Nieto <cmn@elego.de>