Filter out jobs in progress when pruning Db_store

[kit-ty-kate]

Otherwise some jobs can get removed even before it started building if under heavy load for 10 minutes or if there is no output for that long too.

Building on iphito.ocamllabs.io
+++ Timeout!! (1 hour) +++
+++ Job cancelled +++

[MisterDA]

Why does it matter to init preemptive with only one thread (and not use the default)? Do you use this as a kind of queue for database operations?

[kit-ty-kate]

Do you use this as a kind of queue for database operations?

yes

[kit-ty-kate]

I should use mutexes but we can see later. This is a WIP anyway and it's only for testing