[CVS ci] Strings. Finally.

[Leopold Toetsch]

After Dan's string patch got merged to head (thanks to Will Coleda for 
sending me a diff), I've put in some more string stuff with these new 
opcodes:

* charset, charsetname, find_charset
* is_whitespace, is_digit, is_wordchar, is_punctuation, is_newline
* find_whitespace, find_digit, find_wordchar, find_punctuation, 
find_newline, find_word_boundary

There are some tests in t/op/string_cs.t - more are welcome.
The assemblers provide this new syntax for specifying a charset:
  set S0, ascii:"the string"
i.e. a double-quoted string constant can be prefixed by a charset.
Known charsets are currently: ascii, binary, iso-8859-1 (the default).
Have fun,
leo