feature(completion): ng completion made more robust

Fix #2284
Close #2286

Author: catull

Diff for: packages/angular-cli/utilities/completion.sh

@@ -18,7 +18,7 @@ set_opts='--global -g'
 test_opts='--browsers --build --colors --log-level --port --reporters --watch -w'
 version_opts='--verbose'
 
-if type complete &>/dev/null; then
+if test ".$(type -t complete 2>/dev/null || true)" = ".builtin"; then
   _ng_completion() {
     local cword pword opts
 
@@ -47,7 +47,7 @@ if type complete &>/dev/null; then
   }
 
   complete -o default -F _ng_completion ng
-elif type compctl &>/dev/null; then
+elif test ".$(type -w compctl 2>/dev/null || true)" = ".compctl: builtin" ; then
   _ng_completion () {
     local words cword opts
     read -Ac words
@@ -75,6 +75,9 @@ elif type compctl &>/dev/null; then
   }
 
   compctl -K _ng_completion ng
+else
+  echo "Shell builtin command 'complete' or 'compctl' is redefined; cannot perform ng completion."
+  return 1
 fi
 
 ###-end-ng-completion###