long paras + tools/string.hxx

[Caolán McNamara]

The 16 bit length limitation in writer is now removed towards 4.3.

The 16 bit paragraph length limit in editeng still remains, editeng
mixes freely sal_uInt16 with xub_StrLen and has a pile of hard-coded
0xFFFF here and there which makes it tricky to see at a glance which
values are string lengths and offsets and which are not. Sigh.

Also, note there is a hidden limit in tools/stream.hxx of 0xFFFE in
things like ReadLine and ReadByteStringLine and their callers.

sc is now the only module that includes tools/string.hxx and uses
STRING_MAXLEN. It would be great if some calc hackers could have a look
there to see if those limits still make sense (e.g.
nArbitraryLineLengthLimit) especially considering the ReadLine, etc.
issue.

C.