[combine-and-package] Add option to link an arch's libexec/bin dirs to the main bin/libexec dirs.

Emacs doesn't like not being able to find the naked dirs and will complain
with a warning like:

Warning: arch-dependent data dir `/Users/build/workspace/Emacs-Multi-Build/label/mavericks/emacs-source/nextstep/Emacs.app/Contents/MacOS/libexec/': No such file or directory

Also, without this change, users (like me) that had emacsclient linked to
/Applications/Emacs.app/Contents/MacOS/bin/emacsclient will have their
emacsclient break.
[verbose-shell] Add 'ln -s'.
[Heroes.rtf] New donor!
[launch.rb,combine-and-package] Use underscore instead of dot in version numbers to get around codesign bug

The 'codesign' app (from XCode 6.0) dies when it sees something like
'bin-i386-10.5' in the MacOS directory. I believe it thinks the directory is
a framework or some other kind of bundle and it dies when the contents don't
match up with what it expects. I've filed a bug with Apple (18340424) but in
the meantime, if we remove the dots from the name then codesign doesn't get
confused.