nova: fix boot modules and command line bootstrap

Allocate ever an extra page behind the commandline pointer. If it turns out
that this page is unused, because commandline was short enough, unmap the
memory and put the virtual and physical regions back to the allocator.

Fix #664
nova: use bender by default

Bender fixes the serial output on modern PC hardware. Prior this patch,
it was used only when combined with pulsar. Now, we also use it when
booting via GRUB.
nova: Support upgrading kernel via 'make prepare'
noux_tool_chain_nova: Don't restrict to Fiasco.OC

Thanks to @alexab's recent work on base-nova and the NOVA kernel, the
test is expected to run successfully on NOVA too.
demo: Avoid debug message in demo/src/lib/mini_c

The "strncpy - not implemented" message appeared on the use of libpng.
Even though it did not cause trouble, spilling the log with such
easy-to-fix issues should better be avoided.