*) for footprint access into *.mod files and 
*) BOARD save/load

The item_io.cpp and ioascii.cpp have been set off to the side for reference
as *.notused, for awhile.

The CMake options USE_NEW_PCBNEW_LOAD and USE_NEW_PCBNEW_SAVE are gone,
this is now the mandatory usage of the LEGACY_PLUGIN.  This should reduce
code maintenance for awhile until the s-expression plugin comes into 
play.  But at least for legacy format, there is not two code bodies
to maintain any more.

A new LEGACY_PLUGIN footprint library caching scheme is in place which 
needs some testing.  It should not be any faster, but might give better 
results in a networked environment if there is *.mod files on the server.