package daemon: Handle location info request in app thread

* ... instead of queuing it for the job thread. The advantage is that
the request will be handled immediately and clients won't have to wait
for transactions (which may even require user feedback) to finish. It
complicates Volume a bit, since there are now two threads that may
access it. The shared data have been moved to a State object which is
protected by a lock.
* For commit transaction requests check whether another package request
is already pending/in progress before queuing a job. Fail immediately,
if there is.

Fixes bug #10039.

headers/private/package/DaemonDefs.h

@@ -18,6 +18,7 @@ namespace BPrivate {
 
 enum BDaemonError {
 	B_DAEMON_OK = 0,
+	B_DAEMON_INSTALLATION_LOCATION_BUSY,
 	B_DAEMON_CHANGE_COUNT_MISMATCH,
 	B_DAEMON_BAD_REQUEST,
 	B_DAEMON_NO_SUCH_PACKAGE,