[api] using statefs typedefs in the public api

Also changing off_t/size_t/ssize_t to (unsigned) long because this types
size depends on declaration.

TODO: check api types sizes
Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[service] do not setup environment

while this workaround works in some environments it should not
exist. It is better to fix broken environment

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[pkgconfig] configure .pc files

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
fix: non-compat providers: no introspection

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
report exact version of incompatible provider

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