execute: also set SO_SNDBUF when spawning a service with stdout/stderr connected to journald
bus: let's use GREEDY_REALLOC() when allocating space for containers
bus: use GREEDY_REALLOC() when allocating message queues
bus: fix symlink to bus proxy socket
systemctl: properly initialize and free sd_bus_error in "systemctl cat"

We need to properly initialize all error structs before use and free
them after use.

Also, there's no point in flushing stdout if we output a \n anyway...
units: properly make bus proxy socket of type Accept=yes
bus: also mask dbus.service in generator if kdbus is found