convert: check for failed svn import in debugsvnlog and abort cleanly 'hg debugsvnlog' failed with a crash when using the uninitialized transport in get_log_child if the import of the svn libraries had failed. 'convert' should never get as far as launching 'hg debugsvnlog' if the svn libraries are missing, but by launching a subprocess there is risk that the environment is mangled so the second import fails. It is in principle also possible to launch the command manually.