If `nvm_ls` is called without a pattern, and node exists, tack on "system".

nvm.sh

@@ -194,6 +194,9 @@ nvm_ls() {
     echo "N/A"
     return 3
   fi
+  if [ -z "$PATTERN" ] && nvm_has_system_node; then
+    VERSIONS="$VERSIONS$(printf '\n%s' 'system')"
+  fi
   echo "$VERSIONS"
   return
 }

test/fast/Listing versions/Running "nvm ls" should include "system" when appropriate

@@ -0,0 +1,21 @@
+#!/bin/sh
+
+die () { echo $@ ; exit 1; }
+
+. ../../../nvm.sh
+
+mkdir -p ../../../v0.0.1
+mkdir -p ../../../v0.0.3
+mkdir -p ../../../v0.0.9
+mkdir -p ../../../v0.3.1
+mkdir -p ../../../v0.3.3
+mkdir -p ../../../v0.3.9
+
+nvm_has_system_node() { return 0; }
+nvm ls | grep system 2>&1 > /dev/null
+[ $? -eq 0 ] || die '"nvm ls" did not contain "system" when system node is present'
+
+nvm_has_system_node() { return 1; }
+nvm ls | grep system 2>&1 > /dev/null
+[ $? -ne 0 ] || die '"nvm ls" contained "system" when system node is not present'
+