Add utility away_from_zero_round and use it for LESS round()

Also _ophsl should use it when running unter Py3k (instead of
convergent_round).

lesscpy/lessc/color.py

@@ -364,5 +364,5 @@ class Color():
         hls = list(self._hextohls(color))
         hls[idx] = self._clamp(getattr(hls[idx], op)(diff / 100.0))
         rgb = colorsys.hls_to_rgb(*hls)
-        color = (utility.convergent_round(c * 255) for c in rgb)
+        color = (utility.away_from_zero_round(c * 255) for c in rgb)
         return self._rgbatohex(color)

lesscpy/lessc/utility.py

@@ -13,6 +13,7 @@ from __future__ import print_function
 import collections
 import math
 import re
+import sys
 
 
 def flatten(lst):
@@ -246,6 +247,18 @@ def split_unit(value):
     return r.groups() if r else ('', '')
 
 
+def away_from_zero_round(value, ndigits=0):
+    """Round half-way away from zero.
+
+    Python2's round() method.
+    """
+    if sys.version_info[0] >= 3:
+        p = 10 ** ndigits
+        return float(math.floor((value * p) + math.copysign(0.5, value))) / p
+    else:
+        return round(value, ndigits)
+
+
 def convergent_round(value, ndigits=0):
     """Convergent rounding.
 

lesscpy/plib/call.py

@@ -196,7 +196,7 @@ class Call(Node):
             str
         """
         n, u = utility.analyze_number(value)
-        return utility.with_unit(int(round(float(n))), u)
+        return utility.with_unit(int(utility.away_from_zero_round(float(n))), u)
 
     def ceil(self, value, *args):
         """ Ceil number