Initial python3 changes

Mostly just updating libraries, removing string encoding/decoding,
fixing some edge cases. No new functionality was added in this
commit.

lib/yaml/loader.py

@@ -1,12 +1,12 @@
 
-__all__ = ['BaseLoader', 'SafeLoader', 'Loader']
+__all__ = ['BaseLoader', 'FullLoader', 'SafeLoader', 'Loader', 'UnsafeLoader']
 
-from reader import *
-from scanner import *
-from parser import *
-from composer import *
-from constructor import *
-from resolver import *
+from .reader import *
+from .scanner import *
+from .parser import *
+from .composer import *
+from .constructor import *
+from .resolver import *
 
 class BaseLoader(Reader, Scanner, Parser, Composer, BaseConstructor, BaseResolver):
 
@@ -18,6 +18,16 @@ class BaseLoader(Reader, Scanner, Parser, Composer, BaseConstructor, BaseResolve
         BaseConstructor.__init__(self)
         BaseResolver.__init__(self)
 
+class FullLoader(Reader, Scanner, Parser, Composer, FullConstructor, Resolver):
+
+    def __init__(self, stream):
+        Reader.__init__(self, stream)
+        Scanner.__init__(self)
+        Parser.__init__(self)
+        Composer.__init__(self)
+        FullConstructor.__init__(self)
+        Resolver.__init__(self)
+
 class SafeLoader(Reader, Scanner, Parser, Composer, SafeConstructor, Resolver):
 
     def __init__(self, stream):
@@ -38,3 +48,16 @@ class Loader(Reader, Scanner, Parser, Composer, Constructor, Resolver):
         Constructor.__init__(self)
         Resolver.__init__(self)
 
+# UnsafeLoader is the same as Loader (which is and was always unsafe on
+# untrusted input). Use of either Loader or UnsafeLoader should be rare, since
+# FullLoad should be able to load almost all YAML safely. Loader is left intact
+# to ensure backwards compatibility.
+class UnsafeLoader(Reader, Scanner, Parser, Composer, Constructor, Resolver):
+
+    def __init__(self, stream):
+        Reader.__init__(self, stream)
+        Scanner.__init__(self)
+        Parser.__init__(self)
+        Composer.__init__(self)
+        Constructor.__init__(self)
+        Resolver.__init__(self)