issue with the "$" syntax for the drell yan process

[oliviermattelaer]

comment get from Eleni performing the standard basic tutorial:

• the Z peak is not (fully) removed when generating "p p > e+ e- $z"

One can see:

• that the cross-section is reduced compare to p p > e+ e- (so some z suppression are in place)
• that the sum of "p p > e+ e- $ z" and "p p > Z, Z > e+ e-" is much higher than "p p > e+ e-" (so double counting)

The issue is

• that the "$" syntax is implemented via the multi-channel structure of the code and is therefore incompatible with the sde_strategy=2.
• for p p > e+ e-, the default strategy is sde_strategy=2 since only one color is present

The patch ( 9163845) which will be part of 2.9.11 will ensure that the default value for any processes using the "$" syntax would be set to sde_strategy=1