Get rid of clock-raw and use real clock

The clock-raw does not make much sense except internally, using this
clock for seeks and with the public API is more complicated than
necessary.

This patch replaces the clock-raw by a clock-cycles (does not scale the
timestamp with the frequency) and make sure all the calls that
manipulate timestamps use the timestamp in nanoseconds with the offset
applied.
That way the user of the API don't need to bother with the "raw"
timestamp which won't be convenient when dealing with multiple traces
taken in different timezones.

Traces output before and after this patch are exactly the same
and multiple API calls have been tested with real timestamps and
everything seems to work fine.

Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>