Fix many places where malloc failures aren't reported.
Make some API function return an error code. Changing the return type
from void to int is technically an ABI break but should be safe on most
platforms.
- xmlNodeSetContent
- xmlNodeSetContentLen
- xmlNodeAddContent
- xmlNodeAddContentLen
- xmlNodeSetBase
Introduce new API functions that return a separate error code if a
memory allocation fails.
- xmlNodeGetAttrValue
- xmlNodeGetBaseSafe
- xmlGetNsListSafe
Introduce private functions xmlTreeEnsureXMLDecl and xmlSplitQName4.
Don't report low-level errors to the global error handler.
Fix tree
Introduce xmlGetNsListSafe
Fix tree
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