Adding exception for bad column names like "@order:desc"
@order should accept both :DESC and :desc
Undo exception for bad column names

Undo of commit e8c7537514d1432cd154ac35363d97c2d33cdde4
"Invalid" names after : in column names should be accepted,
so that one can construct several where clauses on the same column.
Merge remote-tracking branch 'nitroxy/master' into memcache

Conflicts:
	BasicObject.php
clear_structure_cache fix: don't flush everything

After this patch, it only deletes the keys used for structure cache.
This is important, because I have other caches in memcache that I
want to keep, even when I run migrations that alter db structure.
Fix comment
Merge remote-tracking branch 'p-blomberg/memcache'