String literals with '\0' crash Mars

[Matt Giuca]

Expected:
?> "a\0b"
[97, 0, 98]

Actual:
?> "a\0b"
Uncaught Mercury exception:
univ_cons(univ_cons(software_error("string.from_char_list: null character in list")))

This is due to a call to string.from_char_list in token.m:tok_stringlit, which crashes Mercury if it has a '\0'. Mercury strings may not have null characters in them; Mars strings can. Therefore, the only solution is to change the type of the stringlit constructor from string to list(char), and update all corresponding code accordingly.

[Matt Giuca (mgiuca)]

Fixed in trunk r983.