Add an option to copy task for symlinks

Recent change in Grunt `v1.5.0` has broken our build process, since it copies symlinks as symlinks which is not expected.
Changing copied file contents after copy, changes original file because it is a symlink.

So in fact, it is not backward compatible with the introduced change.

Expected: Symlink should be copied as new file as it was in pre `v1.5.0` version.

Please add an option to support symlink copying for `grunt.copy` task, but it should be `false` by default to not break existing functionality.

Start by tracing the grunt.copy task and the symlink-copy behavior introduced in Grunt v1.5.0. Confirm the default behavior preserves pre-v1.5.0 copying, and verify that changing copied contents no longer changes the symlink target.

Written by the indexing model from the issue text.