SINGA-270 Installation error: include/singa/proto/ is not in /usr/local/include

[xiezl]

Fix the installation path of include/singa/proto.

[moazreyad]

I tried the PR. The directory /usr/local/include/singa/proto/ exists now, but there is a compile error when I try to compile test.cpp from #272 :

$ g++ ./test.cpp -l singa
In file included from /usr/local/include/singa/core/memory.h:24:0,
from /usr/local/include/singa/core/device.h:30,
from /usr/local/include/singa/core/tensor.h:27,
from /usr/local/include/singa/io/encoder.h:24,
from ./test.cpp:1:
/usr/local/include/singa/proto/core.pb.h:17:2: error: #error This file was generated by an older version of protoc which is
#error This file was generated by an older version of protoc which is
^~~~~
/usr/local/include/singa/proto/core.pb.h:18:2: error: #error incompatible with your Protocol Buffer headers. Please
#error incompatible with your Protocol Buffer headers. Please
^~~~~
/usr/local/include/singa/proto/core.pb.h:19:2: error: #error regenerate this file with a newer version of protoc.
#error regenerate this file with a newer version of protoc.
^~~~~
In file included from /usr/local/include/singa/io/encoder.h:25:0,
from ./test.cpp:1:
/usr/local/include/singa/proto/io.pb.h:17:2: error: #error This file was generated by an older version of protoc which is
#error This file was generated by an older version of protoc which is
^~~~~
/usr/local/include/singa/proto/io.pb.h:18:2: error: #error incompatible with your Protocol Buffer headers. Please
#error incompatible with your Protocol Buffer headers. Please
^~~~~
/usr/local/include/singa/proto/io.pb.h:19:2: error: #error regenerate this file with a newer version of protoc.
#error regenerate this file with a newer version of protoc.

[xiezl]

The problem is caused by using two different protobuf libs.
Please make sure you use the same version of protobuf for compiling your own code and the singa code.

[moazreyad]

Ok. I think the problem is fixed now and the PR can be merged. Thank you.

[nudles]

Do we need this one?
I think we agreed to remove it and use it if cmake can detect it.

[nudles]

If cmake detects glog, then we link glog statically into libsinga.so.
In this way, we would not have the linking error when compiling user code.