-# Sources a configuration file if it exists; loads a fallback .local file if
-# it doesn't. If the .local files doesn't exist nothing is sourced.
-#
-# $1: Path to directory where configuration files are located.
-# $2: Directory name in $1 where the non .local files are stored, can be
-# empty. If empty both configuration files (normal and .local) are stored
-# in $1.
-# $3: Base name of file in $2, for example "rc" or "env".
-# $4: Extension for $3, if this file doesn't exist "$1/$3.local" is sourced.
-# Can be empty, then no extension is used.
-# $5: Additional options, set to nolocal to prevent loading of "$1/$3.local"
-# if "$1/$2/$3.$4" doesn't exist.
-#
-# Example with the following directory/file structure, $os is Darwin and
-# $hostname is marvin.
-#
-# ~/.zsh
-# ~/.zsh/env
-# ~/.zsh/env.local
-# ~/.zsh/rc
-# ~/.zsh/rc.local
-# ~/.zsh/host/rc.marvin
-# ~/.zsh/os/rc.Darwin
-#
-# To load additional rc files from within ~/.zsh/rc use the following:
-#
-# source_config ~/.zsh os rc $os # loads os/rc.Darwin
-# source_config ~/.zsh host rc $hostname # loads host/rc.marvin
-#
-# To load additional env files from within ~/.zsh/env use the following (note
-# nolocal to prevent loading env.local two times if os and host files don't
-# exist):
-#
-# source_config zsh os env $os nolocal # loads os/rc.Darwin
-# source_config zsh host env $hostname # loads env.local
-#
-# By letting $4 empty normal configuration files can be sourced. A .local can
-# still be used.
-#
-# source_config zsh "" file # loads zsh/file if it exists
-#
-# Doesn't fit perfectly in this file, but this is the best place to make it
-# available everywhere.
-#
-# If DEBUG is set to a non empty value additional debug output is printed.