[CVS ci] string_str_index

[Leopold Toetsch]

I moved the two - almost identical - <index> op bodys out of core.ops and called this functions string_str_index...

.... and did introduce a new warning WRT const.

- const is currently used in some string.c functions rather inconsistently
- should we remove it alltogether
- introduce a dummy CONST define as hint for the programmer
- insert more const decls (e.g. string_trans_code doesn't modify its src, so ...


leo