install.sh failure, bootstrap = chicken & egg problem

During latest build (from clean Git), I got the following failure:
```
Nimrod build detected
copying files...
cp: cannot stat ‘lib/system/gc_genms.nim’: No such file or directory
```
From looking at the Git history for 'install.sh', I see that it gets rebuilt regularly to fix this kind of bootstrap problems.

I was wondering: wouldn't it be better to
- have csources.zip contain the build.sh to go with _that particular_ bootstrap package
- have "./koch boot" generate the install.sh for the _current_ state of the tree (so it can install files which are actually there)
- have "./koch csource" generate the build.sh to go into csources.zip

In other words:

- _only_ generate a build.sh when the current state is stable enough to bootstrap from, and
- _always_ generate an install.sh which matches the current tree.

This should solve the chicken & egg problem, and neither build.sh nor install.sh need to be tracked by Git anymore.
Any comments, suggestions?