[basic.string]
Change: Non-const .data() member added.
Rationale: The lack of a non-const .data()
differed from the similar member of std::vector.
This change regularizes behavior for this International Standard.
Effect on original feature:
Overloaded functions which have differing code paths
for char* and const char* arguments
will execute differently
when called with a non-const string's .data() member
in this International Standard.
int f(char *) = delete;
int f(const char *);
string s;
int x = f(s.data()); // ill-formed; previously well-formed