fix #32: share/spack/setup-env.sh fails when executed indirectly

fix github #32: share/spack/setup-env.sh fails when executed
indirectly from a symlink

share/spack/setup-env.sh

@@ -152,7 +152,8 @@ function _spack_pathadd {
 # Figure out where this file is.  Below code needs to be portable to
 # bash and zsh.
 #
-_sp_source_file="${BASH_SOURCE[0]}"  # Bash's location of last sourced file.
+_sp_source_dir=$(cd -P $(dirname "${BASH_SOURCE[0]}") && pwd)
+_sp_source_file="$_sp_source_dir/$(basename ${BASH_SOURCE[0]})"  # Bash's location of last sourced file.
 if [ -z "$_sp_source_file" ]; then
     _sp_source_file="$0:A"           # zsh way to do it
     if [[ "$_sp_source_file" == *":A" ]]; then