OpenBSD compilation fix: set JAVAC in bundle targets if javac not found and require.gettext is set to true

This solves the following problem which was found on OpenBSD:

bundle:
     [exec] Generating net.i2p.desktopgui.messages_ar ResourceBundle...
     [exec] ERROR - msgfmt failed on locale/messages_ar.po, not updating translations
     [exec] msgfmt: Java compiler not found, try installing gcj or set $JAVAC
     [exec] msgfmt: compilation of Java class failed, please try --verbose or set $JAVAC
     [exec] 9 translated messages.


In OpenBSD 5.4, neither java nor javac are in the PATH.

  you don't have gettext and want the build to continue.

    * Fix restart from config.jsp if no wrapper
    * i2psnark: Elaborate popups

      target "poupdate" to do that.

    * Shitlist: Move HTML renderer to router console,
      add cause parameter for ease of translation,
      tag all causes

      - Tag tunnel status

      - countries.txt: Convert to mixed case, include in update
      - netdb.jsp: Hide all routers by default, sort and tag country names
      - oldstats.jsp: Move to stats.jsp
      - profiles.jsp: Show new DBH times instead of counts
    * Profiles:
      - Track last good and bad lookup times
        and last good and bad store times,
        to prep for floodfill changes
      - Don't reset last-heard-about at router startup
    * Checklist and Android readme fixups

      - Don't save config when checking for updates on configupdate.jsp
      - Rework ConfigRestartBean and tag
      - More tag fixups
      - Add lang=xx for testing
      - Add file for additional tagged strings

      - configui.jsp post-prop fixup

      - Don't hide link to configui.jsp for IE any more
      - Add lang selection on configui.jsp
      - Tag strings in configui.jsp
      - Load console_big.css if lang == zh
      - Add _x() tag for static iniitializers
      - HTML transitional input tags

      - Persistent lang setting with routerconsole.lang=xx
      - Loading any page with ?lang=xx changes the persistent setting
      - Add a custom Jetty handler to load foo_xx.jsp if it
        exists for language xx. This is for jsp files with lots
        of text in them. Otherwise use inline translate methods.
        Not for included jsps.
      - Add a script to create and update messages_xx.po translation
        files, and create ResourceBundles from them
      - Add class to translate strings from cached ResourceBundles
      - Add translate wrappers to HelperBase, FormHandler, and *Renderer,
        so calls can be made from both jsp and java files
      - Add two example translations on configupdate.jsp - one in
        the jsp itself and one in the helper.
      - This is for strings in routerconsole only. Will be expanded
        to other webapps and the router later.