fix #H2081 - named vault guard messages (trunk only)

fix #H2081 - named vault guard messages (trunk only)

     From a bug report, assigning
a vault guard a name such as Marcel could result in messages like
|The Marcel, confused, disappears.
Many of the guard messages had article "the" hardcoded.  This gets rid
of g_monnam() and uses noit_mon_nam() instead.

     I haven't been able to test all the modified messages; it's a pain
trying to get some of them to occur.