LTorrent: log stack trace as _string_

s/getTrace()/getTraceAsString()/
getTrace() returns an array where as getTraceAsString() gives
the trace as string
avoids the notice 'Array to string conversion'.

Signed-off-by: Arjun Sreedharan <arjun024@gmail.com>
Merge pull request #55 from arjun024/master

LTorrent: log stack trace as _string_