Another tool had -10 already. Since 'merge' is clearly a worst-case
tool (internal), lowering to -100 ensures there's plenty of room for
slightly better cases.
* meld - provide labels for the three panes
* diffmerge - add registry key for detection, improve arguments
* beyond compare - add linux version
* winmerge - improve arguments
* araxis - add configuration, including registry key for detection
* misc - provide default priorities for more tools
If there is already a Beyond Compare's instance running when performing a merge
from Mercurial, BCompare.exe will exit immediately and the merge will fail.
Use the /solo switch to make it always wait (it will open each comparison in
it's own window instead of in tabs)
