leak-detective: Whitelist some Botan functions

leak-detective: Whitelist some Botan functions

Due to the mangled C++ function names it's tricky to be more specific.  The
"leaked" allocations are from a static hashtable containing EC groups.

There is another leak caused by the locking allocator singleton
(triggered by the first function that uses it, usually initialization of
 a cipher, but could be a hasher in other test runners), but we can avoid
that with a Botan config option.