ENH: Mark ImageRegistrationHistogramPlotterTest as RUNS_LONG.

11.1 seconds on a modern machine.

Change-Id: Icc9e87cf6f52b5560c2a3b9d507dd6544f124331
DOC: ITK Software Guide Reference Label Fix

This registration example was incerrectly referencing the whole
section on deformable registration instead of the preceeding
example. These two examples had identical labels in the ITK
Software Guide chapter on registration.

Change-Id: I8603229728651d966660a5c348f8f142de1a150e
COMP: Prevent compile-time numeric warnings in Float Exception test

Place constants in external file to prevent compiler from detecting
compile-time numeric error.

Added optional ADDITIONAL_SRC argument for CreateTestDriver macro to
add src that does not contain an expected test.

Change-Id: I65a71250d2c099a0d86644e4f89973e84f261dc0
Merge topic 'FloatingPointExceptionUseExtern'

e0d1a91 COMP: Prevent compile-time numeric warnings in Float Exception test
Merge topic 'SoftwareGuideMultipleLabelLaTeXWarningFix'

4a67ec2 DOC: ITK Software Guide Reference Label Fix
Merge topic 'HistogramWriter-visibility'

eeb5338 ENH: Mark ImageRegistrationHistogramPlotterTest as RUNS_LONG.