better extension directory handling. original fix from

Axel Hecht <axel@pike.org>, modified to include xmlterm in the ``all'' and
``yes'' options by leaf@mozilla.org, r=cls@seawood.org

configure.in

@@ -2568,17 +2568,23 @@ dnl ========================================================
 dnl Need cookie and wallet to build mozilla, this should
 dnl not be the case, 18352 has been filed.
 dnl http://bugzilla.mozilla.org/show_bug.cgi?id=18352
-MOZ_EXTENSIONS="cookie wallet psm-glue"
+MOZ_EXTENSIONS_DEFAULT="cookie wallet psm-glue"
 
 MOZ_ARG_WITH_STRING(extensions,
 [  --with-extensions       Enable extensions (dirs in extensions/)],
-  [ if test "$withval" = "yes" || test "$withval" = "all"; then
-        MOZ_EXTENSIONS="cookie irc wallet psm-glue"
-    elif test "$withval" = "no" || test "$withval" = "none"; then
+  [ MOZ_EXTENSIONS=""
+    for option in `echo $withval | sed 's/,/ /g'`; do
+      if test "$option" = "yes" || test "$option" = "all"; then
+        MOZ_EXTENSIONS="$MOZ_EXTENSIONS cookie irc wallet xmlterm psm-glue"
+      elif test "$option" = "no" || test "$option" = "none"; then
         MOZ_EXTENSIONS=""
-    elif test "$withval" != ""; then
-        MOZ_EXTENSIONS=`echo $withval | sed 's/,/ /g'`
-    fi ] )
+      elif test "$option" = "default"; then
+        MOZ_EXTENSIONS="$MOZ_EXTENSIONS $MOZ_EXTENSIONS_DEFAULT"
+      else
+        MOZ_EXTENSIONS="$MOZ_EXTENSIONS $option"
+      fi
+    done ],
+  [ MOZ_EXTENSIONS="$MOZ_EXTENSIONS_DEFAULT" ] )
 dnl ========================================================
 
 _cpp_md_flag=