Change test-bad-namespace to help make failure more obvious

I've just chased down a memory leak of 24 bytes, which I thought was a
3x8 struct. In the process I noticed that this string was exactly 24
bytes in length. To make it more obvious in potential future problems,
it's now exactly 29 bytes in length (which is also prime).
Cleanup to avoid a memory leak, fixes  anchor/libmarquise#7

This addresses the latter two failure cases, catching interesting
failures between the C and Python layers.