Allow supplying own config

Ideal for servers in contained environments where writing to $HOME would
not be not considered polite.

bin/notifirc

 #!/bin/bash
 
+#
+# Extra defaults file
+#
+# Options here override /etc and ~/, but are overrided
+# by command line options.
+#
+NOTIFIRC_RC=${NOTIFIRC_RC:-}
 
 usage() {
     #
         echo "will JOIN the channel first."
         echo ""
         echo "Defaults for options can be defined as POSIX shell assignments under"
-        echo "/etc/notifirc.rc or ~/.notifirc.rc. (E.g. 'nick=jdoe', 'max_width=40')."
+        echo "/etc/notifirc.rc, ~/.notifirc.rc or file specified by NOTIFIRC_RC"
+        echo "envvar. (E.g. 'nick=jdoe', 'max_width=40')."
         echo ""
         echo "All is logged under /var/log/notifirc.log, ~/.notifirc.log, or"
         echo "/tmp/notifirc.log, whichever $self can write to."
 
     load_defaults /etc/notifirc.rc
     load_defaults "$HOME/.notifirc.rc"
+    load_defaults "$NOTIFIRC_RC"
 
     while true; do case $1 in
         -c) context=$2; shift 2 || usage ;;