make split_value_list() sane

don't count parentheses, don't nest quotes, don't create empty elements,
let backslash uniformly escape. in short, behave like a sane parser.

Change-Id: I29252fbe14fd6d28217450ec41cf8acfb2e30681
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>