Full thread display for pstree an option

Full thread display for pstree an option

Commit [9de89a] made pstree show the correct thread names. This had
the unintended consequence of making a lot of thread views
uncompact, as the names would be different.

Allan suggested that if you want to see the real thread names, then
explictly ask for them. I agree and pstree now has a new option -t
for showing thread names.

$ pstree 22603
udisksd───4*[{udisksd}]
$ pstree -t 22603
udisksd─┬─{cleanup}
        ├─{gdbus}
        ├─{gmain}
        └─{probing-thread}

References: [#33] https://sourceforge.net/p/psmisc/patches/33/
Signed-off-by: Craig Small <csmall@enc.com.au>