use dd and lmdd for proper direct/buffered IO on linux and irix

Merge of master-melb:xfs-cmds:29214a by kenmcd.

171

@@ -29,6 +29,7 @@ _cleanup()
 # get standard environment, filters and checks
 . ./common.rc
 . ./common.filter
+. ./common.filestreams
 
 # real QA test starts here
 _supported_fs xfs
@@ -36,8 +37,6 @@ _supported_os IRIX Linux
 
 _require_scratch
 
-. ./common.filestreams
-
 _check_filestreams_support || _notrun "filestreams not available"
 
 # test large numbers of files, single I/O per file, 120s timeout