- Don't let disabled TAPs be set as the current target

 - Improve "targets" output:
    * Remove undesirable "chain position" number; we discourage using them
    * TAP and Target column updates:
       + make them long enough for current usage
       + improve labels, removing guesswork
       + "TapName" label patches scan_chain output
    * Highlight the "current" target
    * Display "tap disabled" as a new pseudo-state
    * Update docs accordingly

git-svn-id: svn://svn.berlios.de/openocd/trunk@2107 b42882b7-edfa-0310-969c-e2dbd0fdcd60