Bugfix: xgboost</lib/native/libhdfs.a: could not read symbols: Bad value

[loadingvx]

For Hadoop_CDH distribution (yum installed), there exists no libhdfs.so(dynamic lib) just libhdfs.a(static lib).
A switch "HADOOP_CDH_BINARY" is added for this situation, it enables static compiling, so xgboost
wil not search for libhdfs.so anymore while running.

[tqchen]

@loadingvx may I know the progress on this issue? Thanks

[loadingvx]

I made a contact with HADOOP_CDH developer to make sure this is really a bug or problem. They said
"We currently don't ship any usable natives in the tar-ball, and the files would need to be manually compiled for your platform."
This made me thinking about whether this PR is really a "fix", any way I tried a few times of putting hdfs.a into DMLC_LDFLAGS, but it fails me.
libxgboostwrapper.so can be compiled, but import error occurs duo to hfsxxx can not found.
At the mean time, xgboost works well. This really confused me.
For libxgboostwrapper.so:
gcc -o wrapper.so dmlc.a hdfs.a : compiling error.
gcc -o wrapper.so hdfs.a dmlc.a : compiling ok, import error.

I'm giving up on this issue duo to lessing knowledges about gcc, and any way libxgboostwrapper never be usable. No perfect plan there.

It's ok to just put a warning into README.md :

 "If you are using Hadoop-CDH installed by a tar-ball, please visit [ http://archive.cloudera.com/cdh5/] and download a rpm tar-ball, using the libhdfs.a/libhdfs.so from it. for more informations see [https://issues.cloudera.org/browse/DISTRO-712] "

[tqchen]

Thanks for investigating this! I think we can go with your suggestion.