Added a _cast implementation so that the expression (x:string) produces the same string as write(x).
Added a _cast implementation so that the expression (x:string) produces the same string as write(x).

Did so by invoking x.writeThis on a StringClass instance.

This ensures that casting a range to string generates a bounded-sized string,
rather than a string showing the range's represented sequence
(as it was before).

Also provided a default expression for StringClass's field,
for convenience.


git-svn-id: 88467cb1fb04b8a755be7e1ee1026be4190196ef@19183 3a8e244f-b0f2-452b-bcba-4c88e055c3ca

hildeth/chapel,sungeunchoi/chapel,hildeth/chapel,hildeth/chapel,chizarlicious/chapel,hildeth/chapel,chizarlicious/chapel,CoryMcCartan/chapel,hildeth/chapel,sungeunchoi/chapel,chizarlicious/chapel,chizarlicious/chapel,chizarlicious/chapel,sungeunchoi/chapel,chizarlicious/chapel,sungeunchoi/chapel,CoryMcCartan/chapel,CoryMcCartan/chapel,CoryMcCartan/chapel,hildeth/chapel,sungeunchoi/chapel,CoryMcCartan/chapel,CoryMcCartan/chapel,chizarlicious/chapel,hildeth/chapel,CoryMcCartan/chapel,sungeunchoi/chapel,sungeunchoi/chapel,sungeunchoi/chapel