py3: stringify integer with %d instead of bytes()
The unbundle wire protocol command now returns a properly formatted
reply in Python 3.
Differential Revision: https://phab.mercurial-scm.org/D2274
{header}
<title>Error</title>
<description>Error</description>
<item>
<title>Error</title>
<description>{error|escape}</description>
<guid>https://mercurial-scm.org/#error</guid>
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