Certain tools, e.g. compilers, are customarily prefixed with the name of
their target platform so that multiple builds can be used at once
without clobbering each other on the PATH. I was using identifiers named
`prefix` for this purpose, but that conflicts with the standard use of
`prefix` to mean the directory where something is installed. To avoid
conflict and confusion, I renamed those to `targetPrefix`.
I add newt, checking that it cross-builds too.
I update perf to have newt support, and now it's also finding python, whatever
that means. I've not tested if 'python' as buildInputs is enough.
svn path=/nixpkgs/trunk/; revision=31353
