Bugfix for has_stock_record

Stockrecord can be None if loaded with select_related.

Fixes #648
Fixes #690
Merge remote-tracking branch 'remotes/oscar/master'
Whitespace!
Fix basket form issue for group products

The change in 72c3d7cf broke validation for group products as it tested
if the user could add the initial product to his/her basket.  This fails
for group products as they have no stock.
Relocate the 'edit this product' link

Made smaller and moved to avoid shifting the basic page layout.
ProductClass admin now includes inline for ProductAttribute
Housekeeping
Fix facets search in MultiFacetedSearchForm &
fix ProductIndex price type (DecimalField represented in index such as string instead float val)
Resolve conflict & merge with f/fix-search-facets