Rename key.h to key-locator.h. Refs #1089.
Rename key.hpp to key-locator.hpp. Refs #1089.
Rename key.cpp to key-locator.cpp. Refs #1089.
Merge branch 'issue/1089-rename-key-hpp-to-key-locator-hpp'. Refs #1089.
http://redmine.named-data.net/issues/1089