application of patch from nmagnin

This is a cleaned up version of the modifications added by Nicolas
Magning to the AC Dipole library.

    From 7be18db35c8b51cb0d9c280b8e43ac78335aad64 Mon Sep 17 00:00:00 2001
    From: Michel Arruat <michel.arruat@cern.ch>
    Date: Thu, 18 Feb 2016 17:38:13 +0100
    [PATCH] From Nicolas Magnin: support for individual reference file's
    amplifier. Up to now, the library was suported only similar amplifiers
    (sharing the same reference file). Now each amplifier has its own
    reference file.

Signed-off-by: Michel Arruat <michel.arruat@cern.ch>
---
 acdx/lib/libacdx.c |  8 ++++++--
 acdx/lib/libacdx.h | 56 ++++++++++++++++++++++++++++--------------------------
 acdx/lib/libamp.c  | 18 +++++++++++-------
 3 files changed, 46 insertions(+), 36 deletions(-)