When bootstrapping, we're building things without packages being
available, so we can't expect to find them when looking for
dependencies. So, we find them another way, with an environment
variable. This flag is to tell Idris not to worry about missing
dependencies in this situation.
We also need to update the bootstrapping code, to deal with the new
version number format and new flag in the ipkg files for the libraries.
I think it's still safe to build from the previous version though - lets
see if CI agrees!
Packages are now installed in a directory with their version number.
On adding a package directory, we now look in a local 'depends'
directory first (to allow packages to be installed locally to another
project) before the global install directory.
Dependencies can have version bounds (details yet to be implemented) and
we pick the package with the highest version number that matches.
This involves updating the bootstrap code since it needs a fix in
interface resolution. It shouldn't affect the Idris2-boot build though,
since it's in the libraries not the Idris2 source.
