I separated test's main() into a separate file to override Cargo's
requirement for matching crate names. I had to update the build command
to use a special extern reference for test.
Fixes issues caused by #728.
To avoid linking issues with Rust's libtest, the crate for the test
utility was changed to 'uutest'. However, the user doesn't need to see
this so a few hoops were jumped through to make this transparent.
I also updated the make rules to build the individual features first and
then uutils. This makes 'make && make test' look more organized.
Builds the uutils multicall binary containing all utils (except stdbuf)
by default. To only build a subset
`cargo --no-default-features --features <utils>`
can be used.
Whats missing is building the standalone binaries and a mechanism to
automatically disable the build of unix only utils on windows.
