Create nvm_print_npm_version and use that when printing the npm version.

test/fast/Unit tests/nvm_print_npm_version

@@ -0,0 +1,28 @@
+#!/bin/sh
+
+cleanup () {
+  alias nvm_has='\nvm_has'
+  alias npm='\npm'
+  unset -f nvm_has npm
+}
+die () { echo $@ ; exit 1; }
+
+. ../../../nvm.sh
+
+nvm_has() { return 1; }
+OUTPUT="$(nvm_print_npm_version)"
+[ -z "$OUTPUT" ] || die "nvm_print_npm_version did not return empty when nvm_has returns 1, got '$OUTPUT'"
+
+nvm_has() { return 0; }
+npm() {
+  if [ "_$@" = "_--version" ]; then
+    echo "1.2.3"
+  else
+    echo "error"
+  fi
+}
+OUTPUT="$(nvm_print_npm_version)"
+EXPECTED_OUTPUT=" (npm v1.2.3)"
+[ "_$OUTPUT" = "_$EXPECTED_OUTPUT" ] || die "nvm_print_npm_version did not provided '$EXPECTED_OUTPUT', got '$OUTPUT'"
+
+cleanup