issue #2697: have 'make install' set npm shebang to use its node

[trentm]

As discussed on the ticket.

The end of 'make install' looks like this (where my prefix is /Users/trentm/opt/node-master):

...
cp -rf tools/node-waf /Users/trentm/opt/node-master/bin/node-waf
mkdir -p /Users/trentm/opt/node-master/lib/node_modules/
cp -rf deps/npm /Users/trentm/opt/node-master/lib/node_modules/npm
ln -sf ../lib/node_modules/npm/bin/npm-cli.js /Users/trentm/opt/node-master/bin/npm
shebang #!/Users/trentm/opt/node-master/bin/node /Users/trentm/opt/node-master/lib/node_modules/npm/bin/npm-cli.js

[isaacs]

Landed way back on 1cdadb1. Thanks!