Small bugfix for the Signature Series

BIG UPDATE

Added compatility for Peterbilt 389v2

Added Cummins Signature 600 (EGR only, no SCR), future update will add the rest of the ISX EPA 07 (EGR only, no SCR) for trucks that can run them (As usual, no modern truck or non-glider available, I use Fitzgerald Gliding kits as a general reference)
Note : Cummins Signature and the future EPA07 ISX will have it's own sound derived from an older version of Kriechbaum ISX sound, as it sound different since it's a twin-cam design (one for valves, one for injection) instead of single-cam design like it's younger brother, the ISX15.

Modified torque curves of ALL ISX engines to something more realistic (found on International Truck website by pure luck, most have real curves, but some had to be extrapolated from other curves). Note that this means that the advertised power is now calculated at 1800 RPM only, the real power is higher.

Did some modification in the background concerning management of Volvo engines and the ISX15 sound files.

NOTE : If you don't have sound anymore, you must go to the shop and "rebuy" your engine. as the modification I did to make it easier to manage on the long term affected the sound files names themselves.

Updated D11 sound as per Leen update to his sound.

Corrected DD60 interior sound bug with the Kenworth W900

Small price adjustment for the Volvo D13TC

Semi-Integrated Allison transmissions by Boeing73FLY (note : only transmissions actually available are in this mod, as such the 6600 series is not available, and the VNL only have access to the 4000 and the 4500 as per Volvo website).

Added ISX12 sound from Dimitry T800 mod (by kriechbaum according to Dimitry).

Important changes in the background to make for easier management.

IMPORTANT NOTE : IF YOU USE A CUMMINS ISX OR X, BOTH IN 12-LITERS AND 15-LITERS DISPLACEMENT, PLEASE REBUY YOUR ENGINE.
DUE TO THE CHANGES, YOU WILL NOT HEAR ANYTHING UNTIL YOU REBUY THE ENGINE TO REBIND THE NEW DEFINITIONS FILES.

Updated Volvo D11 sound to keep in with latest update by Leen

Added Volvo D11 sound thanks to Leen.

Added Caterpillar 3408 by vsTerminus (only OTR ratings, marine and genset ratings are NOT included in this compilation

Added Caterpillar CX31 transmission by yours truly

Note : if you already have a truck with a D11 in your fleet, you MUST rebuy the engine to have the new sound for it.

Fixed issue with Detroit Diesel Engine sounds not working