This is purposefully rough, 'cause I hope for discussion.

This is a new command to help manage large thread lists.
I started with the idea "I want to find out which thread
has target id 12345", then extended it to also handle the
new concept of thread names (which thread has name 'foo'),
and extra info as well (which thread has extra info that
includes the string "xyz").

The syntax (I'm open to renaming etc.):

   thread tid [NAME | TARGET_ID | EXTRA_INFO]


The output:

   Thread %d has name '%s'  or
   Thread %d has target id '%s' or
   Thread %d has extra info '%s'

The user can then use the given thread id as input to the
thread command, info threads, etc.

Comments?