Follow symlinks when building zip files

[dshivak]

Adding a call to os.path.realpath(source)
in resources/lambdas.py:get_zip_file would allow use of symlinks. Currently symlinks get zipped up without error and fail when deployed.

[Brian Candler]

Also: If an editor leaves around backup files like foo.py~ then these are uploaded as part of the zipfile. It would be good to have an exclusion pattern.