Fix #1498: manpage writer: don't make whole of item in definition list bold if it includes strong node

tests/root/lists.txt

@@ -52,3 +52,12 @@ y. y
 #. z
 
 #. {
+
+definition lists
+-----------------
+
+term1
+    description
+
+term2 (**stronged partially**)
+    description

tests/test_build_manpage.py

@@ -21,3 +21,7 @@ def test_all(app, status, warning):
     content = (app.outdir / 'SphinxTests.1').text()
     assert r'\fBprint \fP\fIi\fP\fB\en\fP' in content
     assert r'\fBmanpage\en\fP' in content
+
+    # term of definition list including nodes.strong
+    assert '\n.B term1\n' in content
+    assert '\nterm2 (\\fBstronged partially\\fP)\n' in content