Remove and ignore generated file src/boot/host-init.r

src/boot/host-init.r is generated by src/tools/make-host-init.r during
the `prepare` build target. Remove the pre-generated file from version
control and add it to the ignore list.
Merge pull request #118 from earl/build-host-init

Remove and ignore generated file src/boot/host-init.r (yep, should not be in the archive -cs)