Everything you need is in the runtime folder, "spine-libgdx\src". No need for a spine .jar.
Are you configuring the Libgdx project correctly? Try running a basic libgdx app first. Then add the spine runtime source.
The only .jars i include after creating an empty java project are the following:
gdx.jar
gdx-backend-lwjgl.jar
gdx-backend-lwjgl-natives.jar
gdx-backend-lwjgl-sources.jar
gdx-natives.jar