This add a new pgp_armor_headers function to extract armor headers from an
ASCII-armored blob, and a new overloaded variant of the armor function, for
constructing an ASCII-armor with extra headers.

Marko Tiikkaja and me.

The latest update introduced some funny whitespace, but since they are
externally maintained files, we add them to the list of files to ignore.

Avoid the use of **, which was only introduced in Git version 1.8.2.

Set per file type attributes in .gitattributes to fine-tune whitespace
checks.  With the associated cleanups, the tree is now clean for git