PolyZ - Compression Library Wrapper

These are two small wrappers that emulate the snappy and zlib APIs.
It allows a program that was only written to support snappy or zlib
to be used with some other compression library instead.

The snappy wrapper can serve as a frontend for bzip2, lz4, lz4hc,
lzma, lzo, and zlib.

The zlib wrapper can serve as a frontend for bzip2, lz4, lz4hc,
lzma, lzo, and snappy.

The POLYZ environment variable must be set to the name of the desired
compressor and support for the library must have been compiled in
otherwise the wrapper will call exit() and end the process.

Typically the wrapper will be used with LD_PRELOAD to allow it to
override any other compression library a program may have been linked
against. Both the wrapper library and the chosen compressor library
must be preloaded together, the wrapper doesn't use dlopen() to find
the compressor.

E.g., to use bzip2 in a program that only supports snappy:
	export LD_PRELOAD=libpzsnap.so:libbz2.so
	export POLYZ=bzip2

Or to use lzma in a program that only supports zlib:
	export LD_PRELOAD=libpzlib.so:liblzma.so
	export POLYZ=lzma