updated from EXTERN_C_BEGIN/END through sys directory

Hg-commit: ee6b7ef2f48ce66402e7e807302de19506ce15df

Remove petscviewer.h from petscsys.h

Much of sys is independent of viewer. Viewer is used in so many other
places that it is now included by petscvec.h.

Hg-commit: 1d745f01618aa51d3043fb1f87b0546f6

Remove petscviewer.h from petscsys.h

Much of sys is independent of viewer. Viewer is used in so many other
places that it is now included by petscvec.h.

Hg-commit: 1d745f01618aa51d3043fb1f87b0546f60e6e730

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Commit after merge.

Hg-commit: a128a87f5736ccbab37df5d559616f8376f7026e

reorg of src/sys directory
directories that define objects now in the classes subdirectory
rename several confusing name directories

Hg-commit: b2612422c63ac4afe82112892d9efda808f3d601