Re: [PATCH 23/24] hash-ll, hashmap: move oidhash() to hash-ll

>   khash.h lets you instantiate custom hash types that map between two
>   types. These are defined as a struct, as you might expect, and khash
>   typedef's that to kh_foo_t. But it declares the struct anonymously,
>   which doesn't give a name to the struct type itself; there is no
>   "struct kh_foo". This has two small downsides:
> 
>     - when using khash, we declare "kh_foo_t *the_foo".  This is
>       unlike our usual naming style, which is "struct kh_foo *the_foo".
> 
>     - you can't forward-declare a typedef of an unnamed struct type in
>       C. So we might do something like this in a header file:
> 
>          struct kh_foo;
>          struct bar {
>                  struct kh_foo *the_foo;
> 	 };
> 
>       to avoid having to include the header that defines the real
>       kh_foo. But that doesn't work with the typedef'd name. Without the
>       "struct" keyword, the compiler doesn't know we mean that kh_foo is
>       a type.