libubootenv: upgrade 0.3.1 -> 0.3.2

This is a bugfix release which includes the following changes:

f4ab25d shared library: Link against zlib
e663439 Always fsync file writes
80b7f31 Treat '=' as an illegal character in variable names
950f541 libuboot_env: fix calculation of usable envsize
fb88032 Correct initialisations in libuboot_configure
20d1ec7 Force writing of environment if default is used
5ca11bd libuboot_env: correct length to usable env size length
cd4a8f1 libuboot_env_store: fix env double-null termination
9510164 uboot_env: fix infinite loop on short read (EOF)

Signed-off-by: Stefano Babic <sbabic@denx.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>