Mimic the old xmlBuffer strcture in xmlBuf to avaoid catastrophic
failures in case of old code directly reading ctxt->input->buf->buffer
Check on all buffer entry points if an error previously occured on
the buffer, and fail the operation if this is the case, the buffer
becomes immutable and unreadable.
When calling xmlParserInputBufferPush, the buffer may be reallocated
and at the input level the pointers for base, cur and end need to
be reevaluated.
* buf.c buf.h: add two new functions, one to get the base from the
input of the buffer, and another one to reset the pointers based
on the cur and base inded
* HTMLparser.c parser.c: cleanup to use the new helper functions
as well as making sure size_t is used for the indexes computations
This was scattered in a number of modules, xmlParserInputPtr
have usually their base, cur and end pointer set from an
xmlBuf used as input.
* buf.c buf.h: add a new function implementing this setup
* parser.c HTMLparser.c catalog.c parserInternals.c xmlreader.c
use the new function instead of digging into the buffer in
all those modules
This also add converter functions between xmlBuf and xmlBuffer
* buf.c buf.h: the old xmlBuffer routines but modified for size_t
and using xmlBuf instead of xmlBuffer
* Makefile.am: add the 2 new files
* include/libxml/xmlerror.h: add an entry for the new module
* include/libxml/tree.h: expose the xmlBufPtr type but not the
structure which stay private
