releasetools: RangeSet.monotonic is not an optional attribute.

'monotonic' has been non-optional since [1] (L-MR1). Fix the comment in
RangeSet.parse(), as well as the use in blockimgdiff.py.

[1] commit 8b72aefb5a.

Test: Generate an incremental BBOTA package.
Change-Id: I7f95231683473b4f0f07f9c83fccc0e36a1340cb

tools/releasetools/blockimgdiff.py

@@ -191,8 +191,7 @@ class Transfer(object):
     self.tgt_sha1 = tgt_sha1
     self.src_sha1 = src_sha1
     self.style = style
-    self.intact = (getattr(tgt_ranges, "monotonic", False) and
-                   getattr(src_ranges, "monotonic", False))
+    self.intact = tgt_ranges.monotonic and src_ranges.monotonic
 
     # We use OrderedDict rather than dict so that the output is repeatable;
     # otherwise it would depend on the hash values of the Transfer objects.

tools/releasetools/rangelib.py

@@ -13,15 +13,22 @@
 # limitations under the License.
 
 from __future__ import print_function
+
 import heapq
 import itertools
 
+
 __all__ = ["RangeSet"]
 
+
 class RangeSet(object):
-  """A RangeSet represents a set of nonoverlapping ranges on the
-  integers (ie, a set of integers, but efficient when the set contains
-  lots of runs."""
+  """A RangeSet represents a set of non-overlapping ranges on integers.
+
+  Attributes:
+    monotonic: Whether the input has all its integers in increasing order.
+    extra: A dict that can be used by the caller, e.g. to store info that's
+        only meaningful to caller.
+  """
 
   def __init__(self, data=None):
     self.monotonic = False
@@ -63,16 +70,18 @@ class RangeSet(object):
 
   @classmethod
   def parse(cls, text):
-    """Parse a text string consisting of a space-separated list of
-    blocks and ranges, eg "10-20 30 35-40".  Ranges are interpreted to
-    include both their ends (so the above example represents 18
-    individual blocks.  Returns a RangeSet object.
+    """Parses a text string into a RangeSet.
 
-    If the input has all its blocks in increasing order, then returned
-    RangeSet will have an extra attribute 'monotonic' that is set to
-    True.  For example the input "10-20 30" is monotonic, but the input
-    "15-20 30 10-14" is not, even though they represent the same set
-    of blocks (and the two RangeSets will compare equal with ==).
+    The input text string consists of a space-separated list of blocks and
+    ranges, e.g. "10-20 30 35-40". Ranges are interpreted to include both their
+    ends (so the above example represents 18 individual blocks). Returns a
+    RangeSet object.
+
+    If the input has all its blocks in increasing order, then the 'monotonic'
+    attribute of the returned RangeSet will be set to True. For example the
+    input "10-20 30" is monotonic, but the input "15-20 30 10-14" is not, even
+    though they represent the same set of blocks (and the two RangeSets will
+    compare equal with ==).
     """
     return cls(text)