[MERGE] Make <report> tag extensible for extra report engines, courtesy of Nicolas...

The processing of <report> tags during XML file
processing is not modular or extensible, which
means that extra reporting engines cannot easily
add custom behavior for <report> records of their
type. By returning the newly created ID in
the tag_report() method we at least allow them
to hook up a monkey-patch without need to copy-
paste the original code.
This patch also allows an extra XML attribute
for webkit headers, because the original @header
attribute is reserved for a boolean value.

bzr revid: odo@openerp.com-20120214135255-a7hyxsoif4jhg6ro

diff --cc openerp/tools/convert.py
Simple merge