Clean up npm integration a little bit

Change-Id: I849f1056d0188aef264777e18270728b1535f61c

README.markdown

@@ -19,7 +19,7 @@ Often I also put in a line to use a specific version of node.
     
 ## Usage
 
-To download, compile, and install the v0.2.5 release of node do this:
+To download, compile, and install the v0.2.5 release of node, do this:
 
     nvm install v0.2.5
 

install.sh

@@ -9,9 +9,7 @@ if [ "x$has" != "x" ]; then
 fi
 cat <<NVM_CODE >>~/.bashrc
 # ADDED BY npm FOR NVM
-NVM_DIR=$dir
-. \$NVM_DIR/nvm.sh
-nvm use
+. $dir/nvm.sh
 # END ADDED BY npm FOR NVM
 NVM_CODE
 

nvm.sh

@@ -46,8 +46,10 @@ nvm()
       make && \
       make install && \
       nvm use $2
-      echo "Installing NPM..."
-      curl http://npmjs.org/install.sh | sh
+      if ! which npm ; then
+        echo "Installing npm..."
+        curl http://npmjs.org/install.sh | sh
+      fi
       cd $START
     ;;
     "deactivate" )