See <http://bts.grml.org/grml/issue528>.
- transform [[ -z $PARAM ]] etc. tests to:
[[ $PARAM -gt 0 ]] and [[ $PARAM -eq 0 ]]
- fix a problem when /etc/zsh/functions.d
- do not load zsh/zprof as it might be loaded already
- *update* the battery status in $RPS1 each time its redrawn.
only happens if the feature is enabled when sourcing zshrc.