Some programs store the executable in a different place and link it
from the `bin` directory. For example, Polari links `$out/bin/polari`
to `$out/share/polari/org.gnome.Polari`. `wrapGAppsHook` did not follow
symlinks so it was not able to wrap Polari, making it unable to access
GObject introspection definitions required for running the program.
I made the wrapping script follow symlinks to fix this corner case.
This change fixes several defects in the way `wrapGAppsHook` selected
the executable to wrap.
Previously, it would wrap any top-level files in the target `/bin` and
`/libexec` directories, including directories and non-executable
files. In addition, it failed to wrap files in subdirectories.
Now, it uses `find` to iterate over these directory hierarchies,
selecting only executable files for wrapping.
