mergetools: improve configuration for several merge tools
* 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
adding b
rev offset length base linkrev nodeid p1 p2
0 0 3 0 0 1e88685f5dde 000000000000 000000000000