…d of strings

This is generally cleaner: less eval, less worrying about separators,
and probably also faster. I got the idea from that python wrapper
script.

I took some liberties with the flags-echoing code to make it more
concise and correct. Also, a few warnings in findInputs and friends I
skipped because I am going to rewrite those anyways.

Thanks @grahamc for telling me about this great linter!

It now blows up on null byte in file (rather than silently truncating),
and invalid arguments (rather than silently skipping).

Also remove useless quotes on same line

foo=$1 surprisingly doesn't need quotes in Bash. Word splits are only
syntactic in string variable (not array var!) assignments.

@dezgeg made the good point that the reasons for doing this were not at
all intuitive.

Stdenv setup misc cleanups