Allow posting filenames of retina images with svn.
When adding or changing files whose filenames include '@' (such as

image@2x.png), we need to clarify in our 'svn info' command line that the '@'

in the filename isn't a revision indicator. This is done by adding an extra '@'

at the end of the filename.

Added a file called image@2x.png and ran 'rbt post --debug'. Saw that there

were no longer a bunch of errors running 'svn info'.