npm checks only node.exe and not node on local dir

npm find local node.exe on windows, but relies on global node
installation on linux. Added a test to check for a local installation of
node before relying on the system wide installation.

Close: #200

Author: rgoulais

bin/npm

@@ -8,6 +8,9 @@ case `uname` in
 esac
 
 NODE_EXE="$basedir/node.exe"
+if ! [ -x "$NODE_EXE" ]; then
+  NODE_EXE="$basedir/node"
+fi
 if ! [ -x "$NODE_EXE" ]; then
   NODE_EXE=node
 fi