FIX4x.xml from quickfixengine.org 
FIX5x.xml from http://sourceforge.net/projects/quickfix/files/

FIX.xml is a modified FIX50SP2.xml with fields from previous versions.
cf new field attributes 'since' and 'until'.

hfField.xsl: generate hf_register_info list.
hfDecl.xsl : generate fix_field list.
Values.xsl : generate value_string and string_string tables.
hfList.xsl : find the last tag number.

packet-fix.h: Values.xsl hfDecl.xsl hfField.xsl output on FIX.xml follow
by output of hfList.xsl on FIX40.xml to FIX44.xml
example
(xsltproc Values.xsl FIX.xml ; xsltproc hfDecl.xsl FIX.xml; xsltproc hfField.xsl FIX.xml;\
xsltproc hfList.xsl FIX40.xml; xsltproc hfList.xsl FIX41.xml; xsltproc hfList.xsl FIX42.xml;\
xsltproc hfList.xsl FIX43.xml; xsltproc hfList.xsl FIX44.xml) > packet-fix.h

NOTES:
- fix_field structure should use 'since' and 'until' attributes for removed
tags.

TODO:
 - make packet-fix.h autogenerated