docs: Add information for mixed ipv4/v6 and NATs.
Merge pull request #324 from xtreemfs/jdillmann-v4v6-nat-doc

docs: Add information for mixed ipv4/v6 and NATs.
tests: Test on valid data on snapshots when the original files change.
servers: Log error if FileMetadata is missing for the deletion stage.

For COW enabled files, the FileMetadata could be null and resulting in an
unhandled NullPointerException.
servers: Keep snapshot data if a file is deleted (fixes #325).

In case of delete operations files will be closed from the OpenFileTable
explicitly. Versioning, deletion etc. will be handled by EventCloseFile.
OpenFileTableEntry had to be extended to enable the required changes.
docs: Fix parameter order for snapshot examples.
client: fixed compiler warning and indentation in xtfsutil_server
client: Added experimental LD_PRELOAD library.
client: minor xtfsutil fix: when open() is called with O_CREAT, the third mode argument must be specified.
client: Some minor changes for the LD_PRELOAD library to avoid possibly uninitialised global state.
Changed CMAKE_BIN's default to just cmake (assuming it is somewhere in PATH) instead of /usr/bin/cmake (which is only true for some systems).
Merge pull request #327 from xtreemfs/jdillmann-snapshot_fixes

Fix #325: Keep snapshot data when a file is deleted
servers: Modified sort host round robin osp to be compatible with Java 1.6
Integrated LD_PRELOAD library into the build files (set BUILD_PRELOAD when building the client to generate it).
Merge branch 'master' of https://github.com/xtreemfs/xtreemfs
Fixes #315
Fix for #321
servers: Return DIR hostname as part of the XtreemFS URL. Fixes #317.

If the MRC hostname has been configured, it was erroneously used for
the DIRs hostname as part of a XtreemFS file URL.