Set image origin for debugging
Schema update 

A validation error occurs when xml:base is not allowed
in included files via xi:include
Add darwin/i386 support (experimental)

`file' gives "Mach-O executable i386"
New HTML to XML filter

Before we parse the HTML code from the user, we should make sure
we have well formed XML when feeding this to the luxor parser.
B: calculation of longest word gives luatex error

The margin-top has introduced a glue node. The function did not
expect a glue node, only hlist nodes.

This fixes #46.