Velocity scripts share the same macro namespace

When a macro M is defined in velocity script in a page A, it is available to all velocity scripts in other pages in the wiki.

This can cause problems on concurrency, when it creates race conditions: if pages A and B both define macro M, with the same name but different definition, this situation can happen:

1. A executes defines M
2. B executes defines M
3. A executes the rest of code that uses macro M
4. B executes the rest of the code that uses macro M

At step 3, A will use macro M defined by B, instead of macro M defined by A that it expects.