py3: have bytes version of sys.argv

sys.argv returns unicodes on Python 3. We need a bytes version for us.
There was also a python bug/feature request which wanted then to implement
one. They rejected and it is quoted in one of the comments that we can use
fsencode() to get a bytes version of sys.argv. Though not sure about its
correctness.

Link to the comment: http://bugs.python.org/issue8776#msg217416

After this patch we will have pycompat.sysargv which will return us bytes
version of sys.argv. If this patch goes in, i will like to make transformer
rewrite sys.argv with pycompat.argv because there are lot of occurences.

mercurial/pycompat.py

@@ -43,6 +43,7 b' if ispy3:'
     osname = os.name.encode('ascii')
     ospathsep = os.pathsep.encode('ascii')
     ossep = os.sep.encode('ascii')
+    sysargv = list(map(os.fsencode, sys.argv))
 
     def sysstr(s):
         """Return a keyword str to be passed to Python functions such as
@@ -91,6 +92,7 b' else:'
     osname = os.name
     ospathsep = os.pathsep
     ossep = os.sep
+    sysargv = sys.argv
 
 stringio = io.StringIO
 empty = _queue.Empty