Don't rename \var to <varname>; DocBook is too verbose here.

Do adopt DocBook's <command>, <option>, <envar> names for \program,
\programopt, \envvar.

Add \filenq --> <filename quote="no"> (it has to go somewhere, at
least for now).

Doc/tools/sgmlconv/conversion.xml

@@ -533,12 +533,16 @@
   <macro name="constant">
     <content/>
     </macro>
-  <macro name="envvar">
+  <macro name="envvar" outputname="envar">
     <content/>
     </macro>
   <macro name="file" outputname="filename">
     <content/>
     </macro>
+  <macro name="filenq" outputname="filename">
+    <attribute name="quote">no</attribute>
+    <content/>
+    </macro>
   <macro name="function">
     <content/>
     </macro>
@@ -560,16 +564,16 @@
   <macro name="newsgroup">
     <content/>
     </macro>
-  <macro name="program">
+  <macro name="program" outputname="command">
     <content/>
     </macro>
-  <macro name="programopt">
+  <macro name="programopt" outputname="option">
     <content/>
     </macro>
   <macro name="regexp">
     <content/>
     </macro>
-  <macro name="var" outputname="varname">
+  <macro name="var">
     <content/>
     </macro>
   <macro name="email">
@@ -590,6 +594,7 @@
     </macro>
 
   <!-- minimal math stuff to get by -->
+  <macro name="pi"/>
   <macro name="sqrt">
     <content/>
     </macro>