(A) module_register_adapter() doesn't check microprotocols_add() 
result, whereas it can fails (eg. dict setitem error). 
Example: "import _sqlite3; _sqlite3.register_adapter({}, None)" => 
should raise a TypeError (unhashable type: 'dict').

(B) Connection.set_isolation_level() tries to create the 
string "BEGIN "+isolation_level and the store it as PyString in 
begin_statement. But if the result can not be converted to string, 
Python crashs. Example:

>>> import _sqlite3
>>> c=_sqlite3.Connection("a")
>>> c.isolation_level = u"\xe9"
Erreur de segmentation (core dumped)

Attached patch fix the two bugs.