[MERGE] First string-fix merge

Hi all,
   here's the first merge request for the string-fix branch.
It includes marking String::buf() to unsafeBuf(), introduces the
rawBuf(), termedBuf(), defined() and undefined() methods to String, and
begins the analysis effort on the callers (mostly in ICAP-related
parts).

I've build-, unit- and run-tested it.

Cheers,
        Francesco

-- 
    /kinkie