input-helper: new asserts

Check if we emitted right number of events in emit_events()
input-helper: don't try emit events when eventarray is empty
input-helper: new asserts
input-helper: free eventarray's memory

When using eventarray_add_event, the events are dynamicaly allocated.
Free the using function eventarray_free()

Also free eventarray when client_free is called and propagate
this change into events-test.c
input-helper: remove redundant re-declaration of dbg() macro
input-helper: add test of emitting events

tests using eventarray
input-helper: comment out SEAT_NAME event

Since display and client are not the same process,
calling this event raises into errors because const char *name
is not valid in child.
I commented it out until I figure out how to fix it.
input-helper: better output of eventarray_compare

print argument's difference as bytes and string
input-helper: compare arguments only when events match

When events don't match it very likely that arguments won't match.
In other words, it's useless to compare arguments of two different
events
input-helper: make dbg() more like function

Now is needed to add semi-colon after dbg, like in usual function case.

I used semi-colon, but haven't noticed that there don't have to be
semi-colon.