suzerain: #3080 add version-gen

Lifted from https://lists.gnu.org/archive/html/autoconf/2009-12/msg00056.html

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suzerain: #3080 version-gen based REVISIONSTR

Removes compiled, SVN-only build-aux/svnrev for build-aux/version-gen
supporting SVN, git-svn, and git-only operation.

Removes generation of *_svnrev.h and installed suzerain-revision.h.
Updates library compilation with new revision string.
Updates applications with new revision string.

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suzerain: #3080 towards correct rebuild

Intent is to always have REVISIONSTR drop the right flag
in place, and to provide an explicit dependency to force
rebuild in that circumstance.  TBD on that dependency file.

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suzerain: #3080 add clean hook

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suzerain: #3080 get rebuilds correct

Think this now causes rebuild and relink on revision change
but not needlessly.

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