Description of the problem / feature request / question:

pkg_tar is unable to preserve the mode of files being packaged and makes everything executable by default. The following should be fixed:

• The default mode should be None, not "0555". Making everything executable by default is just wrong. (Implies not passing --mode to build_tar.py in such case.)
• When no --mode is passed to build_tar.py, the actual permissions of the original file (at least on platforms that support POSIX permissions) should be used. (Currently, there is a simple check that forces the mode to either 0644 or 0755.)
• Ability to specify symbolic modes (e.g. 'u+w'), as supported by tar, would be nice.
• Ability to preserve/set XATTRs and/or ACLs would be nice too.

Environment info

• Operating System: Fedora 25
• Bazel version (output of bazel info release): 0.4.5- (@Non-Git) compiled from bazel-0.4.5-dist.zip (sha256 2b737be42678)