Endpoints.java: revert language change in Endpoints.adjacentNode()'s exception message; "does not contain" seems more appropriate even though Endpoints is no longer a Collection.  "is incident to" implies that "Endpoints" is really a misnomer for "Edge", which is sort of OK for Graph but not so much for Network, and "contain" works in both cases.
Endpoints.java: revert language change in Endpoints.adjacentNode()'s exception message; "does not contain" seems more appropriate even though Endpoints is no longer a Collection.  "is incident to" implies that "Endpoints" is really a misnomer for "Edge", which is sort of OK for Graph but not so much for Network, and "contain" works in both cases.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=129924124

rgoldberg/guava,typetools/guava,tli2/guava,mosoft521/guava,berndhopp/guava,google/guava,google/guava,mosoft521/guava,Xaerxess/guava,xasx/guava,google/guava,rgoldberg/guava,tli2/guava,berndhopp/guava,typetools/guava,mosoft521/guava,Xaerxess/guava,DavesMan/guava,xasx/guava,EdwardLee03/guava,DavesMan/guava,EdwardLee03/guava