Warning fixes - key handling

Warning fixes - key handling

Various warning fixes related mostly to the different types used
to handle keys.  This should clear most of the remaining warnings
in this area.  The technique of inline converter helpers is
extended to cover a few more cases.

README.WARNINGS is adjusted to reflect the current status.

Fixes:
- bos: define and use an inline converter from a ktc key to a bozo key
- bos.c and bos_utils.c should no longer have warnings - adjust Makefile
- define a ktc key to char * converter and use it in a few places
- define kas key to bozo key ptr converter and use it in a few places (afs_bosAdmin)
- cast a few arguments to ka_StringToKey which expects non-const pointers
Change-Id: I1c19869ac232d78209126d4eeeb11af8bcb95815
Reviewed-on: http://gerrit.openafs.org/860
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>