Debugger: Change default gdb engine breakpoint "path usage" to "full"

Setting breakpoints by file name and line does not work robustly when
using gdb, with neither the full path, nor with just the baseline. Since
typically one of the options work, Creator offers a per-breakpoint choice
of which approach to use. Traditionally, using the full path broke more
often, so the default was "short". Lately (gdb 7.3+) using the full path
seems to be more robust, so the default should be changed. Manual
overriding to "short" is still possible.

Change-Id: I9e857c86a63964bdacf9bebc5444ea752e5974f8
Reviewed-by: hjk <hjk121@nokiamail.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>