In 4.3.25-beta we've improved Select All (ctrl+A) to select more and more each time it is pressed (as it does for selecting keys in the graph and dopesheet).
If you have a mesh selected, it selects all vertices, then all meshes.
If you have a bone selected, it selects all children, then all siblings, then all bones.
If the last view you clicked was the tree (the tree tab will have an underline) then it selects all of the same type of item there. For example, if you select a transform constraint and ctrl+A, it will select all transform constraints.
