tt/mini_isam: add new isam_prototypes.h include file and fix up problems

tt/mini_isam: add new isam_prototypes.h include file and fix up problems

There were a variety of potential 64b problems due to the complete
lack of prototype declarations.  So, we add a file, isam_prototypes.h,
generated mostly by the 'cproto' tool.

We also fixed up some errors that having proper prototypes pointed
out, mainly in passing ints where pointers were expected and vice
versa.  The iserase() function was supposed to accept a char *, but
was defined as only accepting a char.  Fun stuff like that.