docs/manual/advanced-dataaccess.xml: Don't imply that it's okay to unconditionally change buffer data or buffer metad...

Original commit message from CVS:
* docs/manual/advanced-dataaccess.xml:
Don't imply that it's okay to unconditionally change
buffer data or buffer metadata in a pad probe callback,
and a bunch of other comments. Fixes #430031.
2 files changed