helper/init: Handle compressed modules transparently.

helper/init: Handle compressed modules transparently.

Detect libz and, if present, define HAS_LIBZ and add -lz to Makefile's
LIBS variable.

Add entry on optional zlib package requirement.

Detect both uncompressed and gzipped kernel modules.

Some Linux distros (like ArchLinux) use gzipped kernel modules with
filenames like ext2.ko.gz.  This change modifies the filename pattern
from (e.g.) "ext2.ko" to "ext2.ko*".

When available, use libz to read the module.

The init_module system call requires uncompressed kernel module bytes.
On some systems (e.g. ArchLinux) the modules are gzipped on disk.
Libz is used to read and uncompress gzipped disk files (*.ko.gz) or
transparently read uncompressed modules (*.ko).