Now check on both the result code and the content type of the
reply. If the content-type is not applicaton/xml do not accept the
answer even if the status code is good.
This fixes https://github.com/owncloud/mirall/issues/92

Loosely based on the logic in csync_vio_init

This fixes a compiler warning about not returning a value

Also make sure to copy destpath, to avoid double free.

sqlite only handle signed integer,  in case of overflow, we numbers are
transformed to floating point, resulting in wierd errors.