Add ability to change backtrace output directory

[Former user]

Revision 990 (76b38815c721) changed backtraces to be put into the log directory, but it should probably be in the bt directory instead, as to not clutter the logs directory unnecessarily.

The backtrace script will have to create the bt directory if it doesn't exist.

[Former user]

Removing version: 1.5.0 (automated comment)

[Joris]

patch uses mkdir -p to create the directory if it does not exist yet. It does no chmodding since i have not seen such a thing anywhere else in asss.

[Former user]

Applied patch in Wiki macro error: Changeset b274857d71c0 not found..