Back-port commit 53dfc43f from inc-unsigned-md

[iay]

The inc-unsigned-md repository includes (or, as of a few days ago, included) a copy of inc-meta. It was originally copied from the incommon-v9 tag but commit 53dfc43f makes three changes:

• Added some targets to inc-meta/build.xml
• Added inc-meta/mdx/incommon/import_sign.xml
• Added inc-meta/mdx/incommon/sign.xml

We should pull back an edited version of that commit so that it will be easier to move forward.

[iay]

Done, commit 793d15d.

Process:

• In inc-unsigned-md, git format-patch -1 53dfc43f
• Hand-edit resulting patch file to just include the three files we want to change, at the root of the repository.
• Hand-edit to fix some tab vs. spaces conventions issues in the resulting files.
• In inc-meta, git am <0001-Sign-output-aggregates.patch