We only looked at the dependencies of a package that are needed for building,
but for detecting build cycles we also have to look at all transitive deps.
Unless the dependency is already finished, then we can ignore its build deps,
even if they are not finished yet.
The test shows such a case where things indirectly create a cycle via cmake.
Fixes#91
Before uploading the status file we make a cached request for the old status
content and if there is no difference we don't upload anything.
This reduces the amount of write API calls and the amount of useless
packages.msys2.org refreshes a bit.
