When installed, default.json is searched for in source dir

[wdconinc]

When installing with cmake --install build/ per the README.md, the default.json config is still searched for in CMAKE_SOURCE_DIR/config, which may be deleted by then.

$ cli_npc
variable NOPAYLOADCLIENT_CONF not set. Using default...
config file does not exist: /opt/spack/stage/wdconinc/spack-stage-nopayloadclient-0.0.3-a7e6k2zequnwdljdsgwtvjf3m4kc7cty/spack-src/config/default.json

Possible solution may be to treat PROJECT_CONFIG_SEARCH_PATHS in config.h.in as a colon-separate search path, and iterate over it in config.cpp.

(Related, default.json is not installed into the prefix.)