As iPXE header files are not C++ compatible, the implementation missed
proper include directives. For example, alloc_memblock() had a wrong
signature, which was not detected. Now, C wrapper functions are
implemented using a local API to the C++ backend.
Related to #593.
This patch reflects eventual allocation errors in a more specific way to
the caller of 'alloc_aligned', in particular out-of-metadata and
out-of-memory are considered as different conditions.
Related to issue #526.
After this commit "make prepare" uses HTTP, HTTPS, or FTP where possible
fvor downloading third-party source codes. This prevents problems with
strict firewall rules where only selected ports are usable.
Unfortunately, git.l4android.org does not support Git via HTTP and,
therefore, the sources need a working Git port (9418).
Fixes#443.
