DRTVWR-447: Introduce LLManifest.process_either().

process_directory() and process_file() are reached both from the top-level
caller (try_path(), a local function within LLManifest.path()) and recursively
from process_directory(). Both places tested os.path.isdir(source), and if so
called process_directory(), else process_file(). Both places were wrong, as it
turns out.

os.path.isdir(symlink_to_directory) returns True. That meant that despite
explicit logic in ccopymumble() to recreate symlinks in the destination area,
we were consistently recopying the contents of symlinked directories.

The downside to this -- in addition to inflating the size of the installer! --
is that macOS is very particular about the structure of a Framework bundle. It
*must* include a Versions/Current symlink identifying which of the other
Versions subdirectories is, in fact, current. If Current is itself a
subdirectory, codesign can't figure out how to sign the framework, and fails.

The logic for deciding between process_directory() and process_file() must
explicitly check for os.path.islink(source). Rather than replicating that
change in both places, introduce process_either() which decides how to forward
the call, and call it both from try_path() and from process_directory().