two tweaks noticed in testing

Exported TMPDIR from sbopkg.conf.

Worded the error message on mktemp failure to hopefully be more helpful
by suggesting a likely cause of failure.

src/etc/sbopkg/sbopkg.conf.new

@@ -23,7 +23,7 @@ SRCDIR=${SRCDIR:-/var/cache/sbopkg}
 # /tmp is not a suitable containing directory, pass in an alternate
 # TMPDIR or modify the following variable. This is actually a mktemp(1)
 # variable.
-TMPDIR=${TMPDIR:-/tmp}
+export TMPDIR=${TMPDIR:-/tmp}
 
 # Other variables:
 CLEANUP=${CLEANUP:-NO}

src/usr/sbin/sbopkg

@@ -4575,8 +4575,13 @@ fi
 # Check for a good config file and set initial variables
 config_check
 
-SBOPKGTMP=$(mktemp -td sbopkg.XXXXXX) ||
-    { echo "$SCRIPT: failed to create sbopkg's temporary directory"; exit 1; }
+SBOPKGTMP=$(mktemp -td sbopkg.XXXXXX) || {
+cat << EOF
+$SCRIPT: failed to create sbopkg's temporary directory
+Do you need to create the parent directories first?
+EOF
+exit 1
+}
 STARTQUEUE=$SBOPKGTMP/sbopkg-start-queue
 USERQUEUE_LOCK=$SBOPKGTMP/sbopkg_user_queue.lck
 MISSING_LIST_FILE=$SBOPKGTMP/sbopkg_addall_missing