bugfix: fix GH move/copy incorrect 200 vs 201 resp
bugfix: fix GH move/copy incorrect 200 vs 201 resp

 * Fix bug introducted during cross-branch rewrite.  200 vs 201 is
   determined by whether the *destination* path exists, not the source.

CenterForOpenScience/waterbutler,rdhyee/waterbutler,Johnetordoff/waterbutler,TomBaxter/waterbutler,felliott/waterbutler,RCOSDP/waterbutler