use a subshell instead of setting the START var

also don't try to install npm if node installation fails.

nvm.sh

@@ -36,21 +36,25 @@ nvm()
         nvm help
         return;
       fi
-      START=`pwd`
-      mkdir -p "$NVM_DIR/src" && \
+      if (
+        mkdir -p "$NVM_DIR/src" &&
         cd "$NVM_DIR/src" && \
         wget "http://nodejs.org/dist/node-$2.tar.gz" -N && \
         tar -xzf "node-$2.tar.gz" && \
         cd "node-$2" && \
         ./configure --prefix="$NVM_DIR/$2" && \
         make && \
-      make install && \
+        make install
+        )
+      then
         nvm use $2
         if ! which npm ; then
           echo "Installing npm..."
           curl http://npmjs.org/install.sh | sh
         fi
-      cd $START
+      else
+        echo "nvm: install $2 failed!"
+      fi
     ;;
     "deactivate" )
       if [[ $PATH == *$NVM_DIR/*/bin* ]]; then