BUG: restore gnu aligned attribute

The test for detecting gnu aligned attribute was always generating the
following compilation error:

Modules/Core/Common/CMake/itkCheckHasGNUAttributeAligned.cxx:27:
error: 'foo<T>::foo() [with T = int]' is private

This feature is now restored.
PERF: Store indexed outputs in array for constant time access

Add vector of iterators into the named outputs in the
ProcessObject. This will provide direct constant time access to the
outputs of filters with out doing string comparisons or lookups into a
map.

Wrote tests to improve coverage of the inputs operations.

Change-Id: If62aa34cbb7a46a7df2c17614f6d3c23508ccfbb
Merge topic 'ProcessObjectIndexNamedOutputs'

4cc805f PERF: Store indexed outputs in array for constant time access
Merge topic 'ResotreGNUAttribueAligned'

2f96c57 BUG: restore gnu aligned attribute