libcap: fix target install

/usr/lib/libcap.so.* was installed via "install -D" but libcap.so.2 is
a symlink so it was dereferenced.

Also update the buildsystem patch so that the shared lib is +X.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>