Bug introduced in commit 675464b1.  On an OOM, this would try to
dereference a char* and free the contents as a pointer, which is
doomed to failure.

Adding a syntax check will prevent mistakes like this in the future.

* cfg.mk (sc_prohibit_internal_functions): New syntax check.
(exclude_file_name_regexp--sc_prohibit_internal_functions): Add
exemptions.
* daemon/remote.c (remoteRelayDomainEventIOError)
(remoteRelayDomainEventIOErrorReason)
(remoteRelayDomainEventGraphics, remoteRelayDomainEventBlockJob):
Use correct free function.