[ckan-dev] A couple of bug fixes to cherry-pick into 1.8

[Sean Hammond]

Hi Adria,

I'd like these two to get into 1.8 if possible, needed for CMAP:

Fix for relative url being used when doing file upload to local storage
cfdeb919f228f917b287eda203e5a5371e0977bc

group controller: use extras_as_string for group read
a8eedda82c0c4e6a4fea5888e5b7864a4abef39e