Slightly less than half (93 / 210) of the NS_METHOD instances in the codebase
are because of the use of NS_CALLBACK in
nsI{Input,Output,UnicharInput},Stream.idl. The use of __stdcall on Win32 isn't
important for these callbacks because they are only used as arguments to
[noscript] methods.
This patch converts them to vanilla |nsresult| functions. It increases the size
of xul.dll by about ~600 bytes, which is about 0.001%.
