port over DB's overhaul of safe_tempnam() and his changes to

port over DB's overhaul of safe_tempnam() and his changes to
check_operating_dir() to make it use boolean values (plus a few more
boolean-related tweaks of mine); also stop wrapping the bad_chr
parameter of parse_mbchar() in #ifdefs for cleanliness, as the
allow_tabcomp parameter of check_operating_dir() isn't wrapped in
#ifdefs, and don't set bad_chr to TRUE when we get a null byte in a
multibyte string, as it's not an invalid multibyte character

git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@2316 35c25a1d-7b9e-4130-9fde-d3aeb78583b8