added true enumerated types in loadparm.c. Now we don't need all those

added true enumerated types in loadparm.c. Now we don't need all those
"interpret_security" and similar functions. This also means that
testparm produces string values for these enumerated types rather than
an integer. This was done to make the web interface much cleaner.

While I was doing this I found a couple of very nasty bugs in the
parm_table code. Someone had added a handle_character_set() function
that treated the char** pointer for a P_STRING as an integer! This
would have caused memory corruption for anyone using the "character
set" option. The loadparm code is delicate - please be careful about
using it's more esoteric features!

I've also removed the "coding system" global and made it a
P_STRING. The integer value was never used anywhere in Samba.
(This used to be commit bac6b0daa288e879330e3d585582122bb93a1ffb)