Let disabled targets be ignored during normal operation:

 - In target_examine(), ignore disabled TAPs

 - Reset handling must not poke at them either:
     * fail $target_name arp_* operations on disabled TAPs
     * in startup.tcl, don't even issue the arp_* wait ops 

ZW: removed superfluous braces from the patch to target.c.


git-svn-id: svn://svn.berlios.de/openocd/trunk@2100 b42882b7-edfa-0310-969c-e2dbd0fdcd60