Generalise determination of hacking directory path

Bash needs a special case to determine the dirname of the sourced path
(the hacking dir), but in all other cases, using $0 allows the script to
be sourced also from within the hacking directory, not only from its
parent.

Signed-off-by: martin f. krafft <madduck@madduck.net>

hacking/env-setup

@@ -3,11 +3,12 @@
 #    modifies environment for running Ansible from checkout
 
 # When run using source as directed, $0 gets set to bash, so we must use $BASH_SOURCE
-if [ -n "$BASH_SOURCE" ] ; then
-    HACKING_DIR=`dirname $BASH_SOURCE`
-else
-    HACKING_DIR="$PWD/hacking"
-fi
+case "$0" in
+    (bash)
+        HACKING_DIR=${BASH_SOURCE%/*};;
+    (*)
+        HACKING_DIR=${0%/*};;
+esac
 # The below is an alternative to readlink -fn which doesn't exist on OS X
 # Source: http://stackoverflow.com/a/1678636
 FULL_PATH=`python -c "import os; print(os.path.realpath('$HACKING_DIR'))"`