Create option for preserveSymlinks.

[coreyfarrell]

This should be passed on to resolve. From the resolve readme for current releases:

• opts.preserveSymlinks - if true, doesn't resolve basedir to real path before resolving.
  This is the way Node resolves dependencies when executed with the --preserve-symlinks flag.
  Note: this property is currently true by default but it will be changed to
  false in the next major version because Node's resolution algorithm does not preserve symlinks by default.

So maybe babel-plugin-bare-import-rewrite should set preserveSymlinks: false by default and list this a breaking change. master of resolve already has preserveSymlinks: false by default but no releases have been made from master.

Requirements:

• testing strategy to ensure the functionality is well defined and works as expected
• determine what this does/should do in Windows or if it's a noop (specifically junctions)

[coreyfarrell]

I've decided to keep the default for this module true but provide an option for consumers to override. I'd be open to exploring this further but for the next release I don't have time to expand testing for this.

CC @LarsDenBakker