distrib/libsparse: Add new third-party library sources.

This patch adds the sources for libsparse under distrib/

This library is used to handle "sparse partition images", i.e. a compressed
version of partition images that take less storage space by using zlib
compression as well as recognizing empty / filler blocks.

It will be used by the libext4_utils sources that will appear in the
tree soon.

Change-Id: Iceaec58ca96469dd2a54c595726873d87095e88b
21 files changed