Revert "Disable Trajectories with FAR/NEAR"

This reverts commit 88c743664fa54ecfcaff3cf4bdd1ef29908cc027.
Fix g-loading estimate

 - Return actual acceleration variable instead of back buffer
 - 'A body in free fall experiences "0-g"' : exclude gravity from
    g-loading estimate.
computeFARReferenceDrag(): call computeForces_FAR() only once