The xwiki/2.0 and 2.1 renderers break the end macro when the content ends with an odd number of ~

When a MacroBlock has " ~ " as content, the xwiki/2.x render does not do anything specific about that ~. For example, an info macro with content " ~ " will be serialized as:

{{info}}~{{/info}}

The problem is that " ~ " being an escaping character, the content above is actually the macro info with content

~{{/info}}

We need to make sure to properly protect the end macro from the ~.
The difficulty is that in xwiki/2.1 the ~ is not consumed when it's used to escape something which is located in a macro. So doubling the ~~ protects the end macro, but you will actually have ~~ in that macro content. This is something that should ideally be fixed in a xwiki/2.2 syntax, but in the meantime we need to decide the least bad option to stop breaking end macros:

• escape with ~ despite the problem described above: at least it will behave as expected when the macro contains wiki syntax
• add an extra white space after the infamous ~: it's not more valid, but at least the hack is less visible for a human
• a mix:
  • when the Macro indicates that the content type is wiki syntax, escape using ~
  • when we don't know the content type, add an extra white space

Whatever solution, a slightly bad escaping is better that completely breaking the macro...