Merge pull request #9 from deztructor/master

breaking compatibility: functional.visit logic is changed
[sys] cmd line constructor fix

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
functional: first()

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
os: environ(name)

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[os] du should explicitely use Kb as block size

Otherwise environment variables influence calculations

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
more debug tracing

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>