The installer does what amounts to `cp -p`. If the node binary is in use at
the time of the copy, it'd fail with a ETXTBSY error. That's why it's unlinked
first now.
* honor the --without-waf and --without-npm configure switches
* a small logic bug made the installer script install to $PWD instead of
/usr/local if --prefix= was not passed to configure
The old installer was a JS script, which didn't work if node had been
cross-compiled for another architecture. Replace it with a python script.
Fixes#3807.
