Allow openrc to be loaded in zsh

This fix the test then detect OSX in GetOSVersion that break support of zsh.

Fixes bug #1233118

Change-Id: If243fbe59f8f08041327057425018d7ae0d13ab2
diff --git a/functions b/functions
index 83826f9..d9445fe 100644
--- a/functions
+++ b/functions
@@ -364,7 +364,7 @@
 # GetOSVersion
 GetOSVersion() {
     # Figure out which vendor we are
-    if [[ -n "`which sw_vers 2>/dev/null`" ]]; then
+    if [[ -x "`which sw_vers 2>/dev/null`" ]]; then
         # OS/X
         os_VENDOR=`sw_vers -productName`
         os_RELEASE=`sw_vers -productVersion`