avconv_opt: fix avio_open2() return code check

avio_open2() only return < 0 when error.
dnxhdenc: return meaningful return codes
avconv: make the ASCII flow charts narrower to fit onto TTY

These charts in man page are currently destroyed.

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
disable -rpath-link on Solaris

The Solaris -rpath linker option parser is greedy.
build: add Solaris symbol versioning

The Solaris linker does not support globs in linker scripts for
symbol versioning (this is a GNU extension). Let's instead borrow
make_sunver.pl from GCC to make a description file that works
with the Solaris linker.