UseLENDGammaNuclear only available in Geant4.10.4

[Jochem Snuverink]

Introduced in 9f58e4a. The UseLENDGammaNuclear option was only introduced in 10.4 (http://www-geant4.kek.jp/lxr/source/physics_lists/constructors/gamma_lepto_nuclear/src/G4EmExtraPhysics.cc?v=10.4) and should be protected with include guards.

[Laurie Nevay]

Fix Issue #231.

→ <<cset 295834754160>>

[Laurie Nevay]

Thanks for reporting Jochem. Should be fixed now.