As of today, the Mono Debugger is now using the normal `mono' to execute managed code rather than using its own `mono-debugger-mini-wrapper'.
This means that you need a recent SVN version of Mono from either HEAD or the 1-1-13 branch: everything after r55889 is ok.
There are two big advantages of the new setup:
The required mini changes are both in HEAD and in the 1-1-13 branch, so these two versions are explicitly compatible with each other - you can, for instance, use the 1.1.13 Mono to run the debugger and use Mono from HEAD in the target application.