Add wrappers for target->type->examined:

Add wrappers for target->type->examined:
- replace all checks of target->type->examined with target_was_examined().
- replace all setting of target->type->examined with target_set_examined().
- replace clearing of target->type->examined with target_reset_examined().
- add documentation in target_s to warn not to access field directly.

git-svn-id: svn://svn.berlios.de/openocd/trunk@1962 b42882b7-edfa-0310-969c-e2dbd0fdcd60