• Checkout old copy.
• Merge changes from working copy (I love you WinMerge!).
• Check for new files/folders, add them to svn.
• Check that it builds.
• Commit up to date copy.
• Repeat for all known checkouts (there are a 100 or so!)

// File1.cpp
class ClassA
{
    int a;

public:
    ClassA()
    {
         a = 1;
    }

    ~ClassA()
    {
    }
};

void MethodA()
{
    ClassA instance1;
}

// File2.cpp
class ClassA
{
    char *b;

public:
    ClassA()
    {
         b = strdup("Hello");
    }

    ~ClassA()
    {
         free(b);
    }
};

void MethodB()
{
    ClassA instance2;
}