Clean up warnings in libadmin/bos/afs_bosAdmin.c

Clean up warnings in libadmin/bos/afs_bosAdmin.c

Use the correct data structures for BOS timestamps.  Use afs_int32 for
the expressed timestamps for executables since that's what the BOS RPC
says it's using for right now; we should change this, but when we do,
warnings will catch this use along with the others.  Cast some const
char *'s that are passed into BOS functions that take char *'s.

Change-Id: Iff3a6c42241953ed086f8e739cdb344a41a44635
Reviewed-on: http://gerrit.openafs.org/2050
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Tested-by: Marc Dionne <marc.c.dionne@gmail.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>