Fix single point axis helpers

Axes defined with the "vecline" FGD property type should now be properly
compensated. Affects phys_ragdollmagnet, point_angularvelocitysensor,
point_velocitysensor, phys_torque, and phys_motor from base HL2.
Merge pull request #13 from ItEndsWithTens/fix_vecline

Fix single point axis helpers