mercurial.spec: rename docutils to python-docutils in BuildRequires

Even though the name of the project is Docutils, most packagers use
the package name python-docutils to fit into the naming scheme of
other packages written in Python.  The name is used by Fedora, EPEL,
DAG, Mandriva, and a few other distributions.

contrib/mercurial.spec

@@ -17,7 +17,7 b' BuildRoot: %{_tmppath}/%{name}-%{version'
 # python-devel provides an adequate python-dev.  The merge tool is a
 # run-time dependency.
 #
-BuildRequires: python >= 2.4, python-devel, make, gcc, docutils >= 0.5
+BuildRequires: python >= 2.4, python-devel, make, gcc, python-docutils >= 0.5
 Provides: hg = %{version}-%{release}
 Requires: python >= 2.4
 # The hgk extension uses the wish tcl interpreter, but we don't enforce it