[Po4a-devel]Fix encoding attribute handling in Xml.pm

Wine's DobBook documentation is in SGML but I also tried the DocBook.pm module on it. The nice thing is that it translates the 'lang' attribute. The bad thing is that it does not handle including files using entities and this is extensively used in Wine's documentation :-(. Anyway, during this test I added the XML prologue recommended by the DocBook documentation: http://www.docbook.org/tdg/en/html/ch02.html#ch02-makexml <?xml version='1.0'?> <!DOCTYPE book PUBLIC "-//Norman Walsh//DTD DocBk XML V3.1.4//EN" "http://nwalsh.com/docbook/xml/3.1.4/db3xml.dtd"> This caused the Xml.pm module to emit some 'Use of uninitialized value' warnings because the <?xml> tag did not specify the encoding. That was (or seemed) easy to fix so here's an hopefully correct patch: Changelog: * po4a/lib/Locale/Po4a/Xml.pm Francois Gouget <fgouget(a)free.fr&gt; Append the encoding attribute if it is not defined in the <?xml> tag. -- Francois Gouget fgouget(a)free.fr http://fgouget.free.fr/ $live{free} || die "";