Improve devserver durability. Refs #473.

Three changes:

1. Fix inconsistent "pwd" behavior by using make's $(CURDIR) builtin.
2. Change bash shebang to the more-portable form.
3. Tell users when Pelican and SimpleHTTPServer have been backgrounded.

pelican/tools/templates/develop_server.sh.in

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 ##
 # This section should match your Makefile
 ##
@@ -65,6 +65,7 @@ function start_up(){
   python -m SimpleHTTPServer &
   echo $$! > $$SRV_PID
   cd $$BASEDIR
+  sleep 1 && echo 'Pelican and SimpleHTTPServer processes now running in background.'
 }
 
 ###