[HL25] Allow enabling or disabling the default HL1 player models location

[Zarko Dinev]

Currently every single Half-Life mod placed in "Half-Life" folder under Steam will default to using /valve/models/player/*" player models first and then will move to the mod's folder player models.

This might be desirable in some cases, but in others it's not desirable and can actually cause issues. In case the player models for the mod do use custom or modified animations, the default Half-Life player models will not work properly. This can be observed in The Specialists mod, but not limited to this one.

My request is to create a separate liblist.gam variable, that can disable loading the player models from valve, valve_addon, valve_downloaded, valve_hd etc valve_* folders in case the value is set, and to only load player models from the modname/models/player/ folders. This will be really appreciated.