Fix vtkTextActor to prevent truncation of text.

Add Fudge factor to the texture coordinates to prevent the top
row of pixes from being truncated on some systems.

Added actor to TestMathTextFreeTypeTextRenderer and
TestMathTextFreeTypeTextRendererNoMath that demonstrates issue.

Change-Id: Ib55c39583be3dfe946128d9d8ab6536ec32f07c0
Portability fix for windows (fminf() --> std::min())

Change-Id: Ife8f4d2149bee045917344a397626d3c853a4653
Merge topic 'text_actor_cutoff_fix' into master

75a8066e Portability fix for windows (fminf() --> std::min())
566abbe1 Fix vtkTextActor to prevent truncation of text.