[svn] --delete-after wasn't implemented for files retrieved by FTP or corresponding to

[svn] --delete-after wasn't implemented for files retrieved by FTP or corresponding to
files specified on the commandline.  Made --convert-links be ignored when
--delete-after is specified.  Added note about this fact to --delete-after docs
and made general improvements to them, including the clarification that
--delete-after only deletes local files.