WT-1985. Fixed problems with integer packing in Python:

1) Applied special case from C code for POS_2BYTE_MAX + 1.
2) Handle B/b format chars directly. Up to now these would have
   been encoded using default int encoding (so values above
   63 get errors when encoding.

lang/python/wiredtiger/intpacking.py

@@ -89,6 +89,11 @@ def pack_int(x):
     elif x <= POS_2BYTE_MAX:
         x -= (POS_1BYTE_MAX + 1)
         return chr(POS_2BYTE_MARKER | getbits(x, 13, 8)) + chr(getbits(x, 8))
+    elif x == POS_2BYTE_MAX + 1:
+        # This is a special case where we could store the value with
+        # just a single byte, but we append a zero byte so that the
+        # encoding doesn't get shorter for this one value.
+        return chr(POS_MULTI_MARKER | 0x1) + chr(0)
     else:
         packed = struct.pack('>Q', x - (POS_2BYTE_MAX + 1))
         while packed and packed[0] == '\x00':

lang/python/wiredtiger/packing.py

@@ -108,6 +108,16 @@ def unpack(fmt, s):
                 size = 1
             result.append(ord(s[0:1]))
             s = s[1:]
+        elif f in 'Bb':
+            # byte type
+            if not havesize:
+                size = 1
+            for i in xrange(size):
+                v = ord(s[0:1])
+                if f != 'B':
+                    v -= 0x80
+                result.append(v)
+                s = s[1:]
         else:
             # integral type
             if not havesize:
@@ -177,6 +187,19 @@ def pack(fmt, *values):
             if (mask & val) != val:
                 raise ValueError("value out of range for 't' encoding")
             result += chr(val)
+        elif f in 'Bb':
+            # byte type
+            if not havesize:
+                size = 1
+            for i in xrange(size):
+                if f == 'B':
+                    v = val
+                else:
+                    # Translate to maintain ordering with the sign bit.
+                    v = val + 0x80
+                if v > 255 or v < 0:
+                    raise ValueError("value out of range for 'B' encoding")
+                result += chr(v)
         else:
             # integral type
             result += pack_int(val)