commit -- character styles work

[Paul Rohr]

1. Character styles work.  
2. Styles can be based on other styles. 
3. Applying a style clears explicit properties at the same scope. 

  M src/wp/fmt/xp/fv_View.cpp
  M src/wp/ptbl/xp/pd_Style.cpp
  M src/wp/ptbl/xp/pd_Style.h
  M src/wp/ptbl/xp/pp_AttrProp.cpp
  M src/wp/ptbl/xp/pp_AttrProp.h
  M src/wp/ptbl/xp/pp_Property.cpp
  M src/wp/ptbl/xp/pt_PT_ChangeSpan.cpp
  M src/wp/ptbl/xp/pt_PT_ChangeStrux.cpp
  M src/wp/ptbl/xp/pt_Types.h
  M src/wp/ptbl/xp/pt_VarSet.cpp
  M src/wp/samples/Styles.abw

You can probably get away with just doing a full rebuild of the ptbl
subtree.  

I do still need to add logic so applying block styles clears character-level 
properties too (which is about as tricky as it sounds.)

Enjoy!

Paul