NULL after releasing its reference, so it could be released again later.
* No longer attach the source code to StackFrame, but rather to
FunctionDebugInfo. Besides being the more obvious place it also prevents
un-/reloading the source code when stepping. Only disadvantage is that we
never unload the source again yet.
git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@31256 a95241bf-73f2-0310-859d-f6bbb57e9c96