made workaround for implementations of sed that don't understand -E more robust

also made it compatible with POSIX shells

.tmux.conf

@@ -180,7 +180,8 @@ run 'cut -c3- ~/.tmux.conf | sh -s _apply_configuration'
 # if ! printf '' | sed -E 's///' 2>/dev/null; then
 #   if printf '' | sed -r 's///' 2>/dev/null; then
 #     sed () {
-#       command sed "${@/-E/-r}"
+#       n=$#; while [ "$n" -gt 0 ]; do arg=$1; shift; case $arg in -E*) arg=-r${arg#-E};; esac; set -- "$@" "$arg"; n=$(( n - 1 )); done
+#       command sed "$@"
 #     }
 #   fi
 # fi