keep dir timestamps only works on remove handler

[MAProsper]

When the generated sh script is executed with the "keep dir timestamps" option, they are only kept when using the remove_cmd function. All the cp_... variants, such as cp_symlink, cp_hardlink and cp_reflink, lose the directory timestamp.

To fix this the same pre- and post- DO_KEEP_DIR_TIMESTAMPS checks need to be added to the functions surrounding the modification commands.