Reduced the number of realloc calls zlib_mem_inflate(), while
hopefully not overallocating much either.

Forcibly set block->alloc field when decompressing from gzip or
bzip2.  This cures a crash when attempting to compress CRAM with level
6 and higher.


git-svn-id: svn://svn.code.sf.net/p/staden/code/io_lib@3576 ba6f2710-ca9f-427c-89d3-5bf716dbc8e1
1.13.4 release


git-svn-id: svn://svn.code.sf.net/p/staden/code/io_lib@3577 ba6f2710-ca9f-427c-89d3-5bf716dbc8e1
1.13.4 release


git-svn-id: svn://svn.code.sf.net/p/staden/code/io_lib@3578 ba6f2710-ca9f-427c-89d3-5bf716dbc8e1