HDFS file creation does not support O_CREATE && O_EXCL in libhdfs

[Lin, Yiqun]

Hi hdfs-dev,

Currently in libhdfs, we find that hdfs file create operation doesn’t support 
O_CREATE && O_EXCL.

https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs-native-client/src/main/native/libhdfs/hdfs.c#L1148

    if ((flags & O_CREAT) && (flags & O_EXCL)) {
      fprintf(stderr,
              "WARN: hdfs does not truly support O_CREATE && O_EXCL\n");
    }

Anyone who can explain why for this? This semantic is supported in java 
implementation.

Regards,
Yiqun