Parsing used to work on a non null-terminated buffer, inserting a fake null terminator to increase performance.
This makes it impossible to implement fragment parsing that preserves PCDATA contents (as witnessed by some
tests for boundary conditions that actually depended on this behavior).

Since almost all uses result in us allocating an internal buffer anyway, the new policy is to make sure all buffers
that are allocated by pugixml are null-terminated - the only exception now is external calls to load_buffer_inplace
that don't trigger encoding conversion.

git-svn-id: https://pugixml.googlecode.com/svn/trunk@977 99668b35-9821-0410-8761-19e4c4f06640