These are not universal in the protocol so having functions for them
only obfuscates things.

Provide some safety checks when directly accessing the underlying
pointer of streams.

Just have a simply number of bytes argument to avoid a lot of
complexity.

Makes it more readable to write code that needs to know how much
data/space is available in a stream.

We use a lot of lengths given to us over the network, so be more
paranoid about them causing an overflow as otherwise an attacker
might trick us in to overwriting other memory.

This primarily affects the client which often gets lengths from the
server, but there are also some scenarios where the server might
theoretically be vulnerable.

Issue found by Pavel Cheremushkin from Kaspersky Lab.

Provides safety against them accidentally becoming negative because
of bugs in the calculations.

Also does the same to CharArray and friends as they were strongly
connection to the stream objects.

Keep the generic stream classes clean and general.

git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@589 3789f03b-4d11-0410-bbf8-ca57d06f2519

git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@333 3789f03b-4d11-0410-bbf8-ca57d06f2519

git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@12 3789f03b-4d11-0410-bbf8-ca57d06f2519

git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@2 3789f03b-4d11-0410-bbf8-ca57d06f2519