statichttprepo: use URLError.reason directly

0b3f4be5c5bf changed str(inst) to inst.reason[0] all the way back
in 2006. URLError.reason is a str and we should have taken that
attribute in its entirety. I think the code was supposed to be
inst.args[1] for compatibility with ancient Python versions.
Python 2.7 always sets .reason, so it should be safe to use
directly.

Differential Revision: https://phab.mercurial-scm.org/D5715

mercurial/statichttprepo.py

@@ -59,7 +59,7 b' class httprangereader(object):'
             num = inst.code == 404 and errno.ENOENT or None
             raise IOError(num, inst)
         except urlerr.urlerror as inst:
-            raise IOError(None, inst.reason[1])
+            raise IOError(None, inst.reason)
 
         if code == 200:
             # HTTPRangeHandler does nothing if remote does not support