The joints_axes branches need some (fairly straightforward) changes your .ini file, and master and 2.5 won't run with those changes. So i suggest that you copy your foo.ini file to (for example) foo-ja3.ini and make your changes in the ja3 version of your ini. That way you'll be able to go back and forth between ja3 and the regular branches whenever you want to, by starting linuxcnc with the two different .ini files.
I may have missed some ini changes, if something doesn't work let us know (on the mailing list) and i'll try to update these instructions.
Add this section. Change the JOINTS value to however many joints your machine has, and change the KINEMATICS value to whatever kinematics your machine uses (use trivkins if you don't know).
[KINS] JOINTS = 3 KINEMATICS = trivkins
Split all the [AXIS_n] sections into [AXIS_X] and [JOINT_0], [AXIS_Y] and [JOINT_1], etc. Some variables belong in [AXIS_*], some belong in [JOINT_*], and some belong in both.
Many of the axis.N.* pins have changed name to joint.N.*
Since some ini file variables moved from the [AXIS_*] sections to the corresponding [JOINT_*] sections, any references to those variables in the hal file need to be changed to use the new name.