cart build: clean up unneeded files eagerly

Once the bison, binutils and ghc installations have been completed,
remove the sources and build artifacts to free up space for later
work.
cart build: fix incorrect use of find program

The cartridge build script uses find(1) to locate libraries to
remove or strip, but misses many such files.  Fix the precedence
issues to act on more files.
cart build: patch cabal bootstrap to reduce disk usage

The cabal bootstrap script downloads, unpacks, builds then installs
any missing dependencies.  To reduce disk usage both during and
after the build, patch the `bootstrap.sh' script to remove each
compressed tarball after unpack, and each build directory after
install.
cart build: gzip cartridge for better compression than zip
cart build: hardlink ghc in staging area to save space
Merge pull request #5 from frasertweedale/fix/slimmer-cartridge

save space during build and reduce cartridge size