preparatory cleanups for seamless uncompression improvements

unpack_gz_stream_with_info: fix buggy error check
man: fix possible accesses past the end of a string
move seamless uncompression helpers from read_printf.c to open_transformer.c

function                                             old     new   delta
show_manpage                                         153     212     +59
unpack_gz_stream_with_info                           520     539     +19

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
6 files changed