Support for carriage returns inside table cells

Currently if you type carriage returns inside table cells, these are converted to new lines.
The Radeox table syntax does not support new lines.

I think we need to do two things to support this:

1/ Add a \ at the end of line inside tables
2/ Modify TableMacro and TableBuilder (org.radeox.macro.table) to not create a new cell when there is a \ at the end of a line
The code for TableMacro and TableBuilder is in the radeox source code. To get it:

svn co svn://svn.radeox.codehaus.org/radeox/scm/main/trunk radeox

You need to copy that code to com.xwiki.xpn.render.macro, rename the package
You need to modify the reference to the TableMacro class in
src\main\resources\META-INF\services\com.xpn.xwiki.render.macro.XWikiMacro
instead of calling the radeox one, call the one in XWiki