[Click] Can't use String::c_str on const String

[Matt Seitz]

If I declare a variable as type "String const", GCC will not let me use the 
"c_str" member function:

"passing `const String' as `this' argument
of `const char *String::c_str ()' discards qualifiers"

I believe this can be fixed by declaring "String::c_str" as a "const" member 
function.  That is how "std::string:c_str" is declared:

const char *cc() const; // pointer returned is semi-transient
const char *c_str() const { return cc(); }