Bug#748462: uscan: mk-origtargz choke on .xpi files

[Emmanuel Bourg]

mk-origtargz also fails with the tomcat6 and tomcat7 watch files. In
these packages we are monitoring a SVN tag which is an HTML document.
The file downloaded is discarded but the version detected is used by a
script to checkout the SVN repository and create the upstream tarball.

Here is the watch file used:

version=3
opts=uversionmangle=s/_/./g \
 http://svn.apache.org/repos/asf/tomcat/tc6.0.x/tags/
TOMCAT_([0-9_]*[0-9])/ debian debian/orig-tar.sh

This is a common pattern for several packages maintained by the Java Team.