Merge pull request #339 from ryoqun/conditional-bz2-fn

Conditionally define bzip2 error callback function

librocksdb-sys/src/lib.rs

@@ -22,6 +22,7 @@ use libc::c_int;
 
 include!(concat!(env!("OUT_DIR"), "/bindings.rs"));
 
+#[cfg(feature = "bzip2")]
 #[no_mangle]
 pub fn bz_internal_error(errcode: c_int) {
     panic!("bz internal error: {}", errcode);