This patch fixes the zlib decompress sync flush bug as reported in bug tracking.
It also fixes the following minor bugs;
avoids repeat calls to (in|de)flateEnd when destroying (de)compression objects
raises exception when allocating unused_data fails
fixes memory leak when allocating unused_data fails
raises exception when allocating decompress data fails
removes vestigial code from decompress flush now decompression returns all available data.
tidies code so object compress/decompress/flush routines are consistant