swscale: fix an implementation-defined unsigned-to-signed conversion
swscale: fix some undefined signed left shifts

Based on a patch by Michael Niedermayer <michaelni@gmx.at>
swscale: Set alpha to opaque for internal palettes.

Fixes conversion of pal8 to rgb formats with alpha.

Updated references for 2 FATE tests which previously encoded fully
transparent images.

Based on a patch by Baptiste Coudurier <baptiste.coudurier@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.