[PATCH 2 of 2] bundle2: clarify in docstring that header size is for a single header

[Martin von Zweigbergk]

# HG changeset patch
# User Martin von Zweigbergk <martinvonz at google.com>
# Date 1433972967 25200
#      Wed Jun 10 14:49:27 2015 -0700
# Node ID bbdd187f874804577057a36e167a4bef26b66d0d
# Parent  35f10d65ed455063d043e83355d6536d480cfcb9
bundle2: clarify in docstring that header size is for a single header

The docstring for the header size field currently says "The total
number of Bytes used by the part headers", but the size is about a
single header, so let's change it to "header".

diff --git a/mercurial/bundle2.py b/mercurial/bundle2.py
--- a/mercurial/bundle2.py
+++ b/mercurial/bundle2.py
@@ -66,7 +66,7 @@
 
 :header size: int32
 
-  The total number of Bytes used by the part headers. When the header is empty
+  The total number of Bytes used by the part header. When the header is empty
   (size = 0) this is interpreted as the end of stream marker.
 
 :header: