setting PROTOBUF_DIR fails on Ubuntu

[RagnarGrootKoerkamp]

In case there are other people unable to install this on ubuntu, I had to change the PROTOBUF_LIBRARY in CMakeLists.txt from

set(PROTOBUF_LIBRARY "${PROTOBUF_DIR}/lib/libprotobuf.so")

to

set(PROTOBUF_LIBRARY "${PROTOBUF_DIR}/lib/x86_64-linux-gnu/libprotobuf.so")

because the libprotobuf-dev package installs the libprotobuf.so to /usr/lib/x86_64-linux-gnu/libprotobuf.so instead of /usr/lib/libprotobuf.so.

For others: the corresponding value of PROTOBUF_DIR is just /usr/.

[cjain7]

Thanks for sharing this!