Fix issue #4440, "Subversion sets permissions on files, when it shouldn't"

* subversion/libsvn_subr/io.c
  (io_set_file_perms): Set the user read/write bits to make a file read/write,
   instead of merging in the default bits from the current umask.
   Merging bits from the current umask is a bad idea if the file's
   permissions are more restrictive than the umask implies.

Reported by: Attila Nagy


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1537018 13f79535-47bb-0310-9956-ffa450edef68