trace: add comments about tasks to do

/cc @jm

my2to3/fixes/fix_division_trace.py

@@ -7,6 +7,7 @@ from lib2to3.pytree import Node
 from . import BaseDynamicTraceFix
 from my2to3.util import parse_type
 
+# TODO: /=
 
 class FixDivisionTrace(BaseDynamicTraceFix):
   """Rewrites a / b into division_traced(..., a, b)

my2to3/fixes/fix_nested_except_trace.py

@@ -28,6 +28,8 @@ except Exception as e:
   except Exception as e:
     print(e)
   raise
+
+TODO: this does not cover all cases
   """
   basename = "nested_except"
   traced_information = "lineno_parent", "lineno_child"

my2to3/trace.py

@@ -6,6 +6,7 @@ from lib2to3.refactor import get_fixers_from_package, RefactoringTool
 database = "my2to3_traces.db"
 @contextmanager
 def connection():
+  # XXX: do not reopen all the time
   conn = sqlite3.connect(database)
   try:
     with conn:
@@ -19,6 +20,7 @@ tracing_functions = []
 def create_table(table, *columns):
   with connection() as conn:
     v = ', '.join(columns)
+    # BUG: not unique if there are NULL values
     conn.execute(
       "CREATE TABLE IF NOT EXISTS %s (%s, UNIQUE (%s))" % (table, v, v)
     )