There's a reference to /home/tom/ in one of the source documents:
$ make everything
...
xmlto -x MyStyle-chunk-html.xsl -o spec_html html spec-html.xml
warning: failed to load external entity "/home/tom/share/xml/docbook/xsl/1.73.2/xhtml/chunk.xsl"
compilation error: file /tmp/exim/exim-doc/doc-docbook/MyStyle-chunk-html.xsl line 10 element import
xsl:import : unable to load /home/tom/share/xml/docbook/xsl/1.73.2/xhtml/chunk.xsl
7934a3bf (Tom Kistner 2009-06-30 17:36:39 +0000 10)<xsl:import
href="/home/tom/share/xml/docbook/xsl/1.73.2/xhtml/chunk.xsl"/>
commit 7934a3bf04319d8081676f48693a518699a2dcf1
Author: Tom Kistner <tom@???>
Date: Tue Jun 30 17:36:39 2009 +0000
Fix errors preventing compilation
--
Simon Arlott