qapitrace: fix a string search FIXME request

Issue:
TraceLoader::callContains() had the comment

    FIXME: do string comparison directly on trace::Call

The existing code was doing a new/delete of an ApiTraceCall object
in order to use its interface for a string search.

Resolution:
Assuming what was meant by a direct comparison is using C's
strstr/strcasestr functions, that is what's implemented in
this patch.

An alternative would be to use a QString object's API

    return (QString(call->name()).contains(str, sensitivity));

but no timing was done on that.

Testing:
This code is only hit when searching in unloaded frames. Frame 0 is
pre-loaded so this code isn't exercised until the string is searched
in another frame.

Testing was done with case-sensitive and case-insensitive searches.
Compared against existing previous code for same results.

Timing:
Did two searches each of old and new code using "gettimeofday" timing
in TraceLoader::search with the following results searching for a
nonsense string (to search entire trace), case-insensitive:

<pre>
warzone2100 180MB (180664407)     old         new
                                  ------      -------
Total time in seconds:            89.047      16.3269
                                  88.9844     16.3358
</pre>

Signed-off-by: Lawrence L Love <lawrencex.l.love@intel.com>