Remove memory leaks of strings/Unicode objects passed into the character

Remove memory leaks of strings/Unicode objects passed into the character
data and default handlers -- a new reference was being passed to
Py_BuildValue() for the "O" format character; using "N" plugs the leak.

Fixed two other (minor) leaks that occurred on various error conditions.

Removed uses of the UNLESS macro, which makes code hard to read, and is
Evil.