win32: clean up use of two-argument raise

win32: clean up use of two-argument raise

This makes any attempt to port to Python 3 harder, and the new syntax
is supported in 2.4 already.

--- a/mercurial/win32.py	Tue Jan 01 12:50:04 2013 -0600
+++ b/mercurial/win32.py	Tue Jan 01 12:50:23 2013 -0600
@@ -370,7 +370,7 @@
             if e.errno != errno.EEXIST:
                 raise
     else:
-        raise IOError, (errno.EEXIST, "No usable temporary filename found")
+        raise IOError(errno.EEXIST, "No usable temporary filename found")
 
     try:
         os.unlink(temp)