This "portable" mode rewrites the npm shebang to use the "node" executable
in the same directory relative to the "npm" script. This makes the "npm"
script "just work" even when "node" is not in the user's $PATH.
This mode is necessary for the precompiled binary packages that may potentially
be extracted to anywhere. The regular shebang-rewriting logic would normally
set the npm script's shebang to "/bin/node" which will not be present on anyone's
machine. In the end, we want the precompiled packages to be as user-friendly as
possible.
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.
