Footprint library table improvements.

* Add save table and set project path environment variable code to
  FP_LIB_TABLE object.
* Add code to Pcbnew and CvPcb to set project path environment variable.
* Create empty footprint table in Pcbnew when new board created.
* Save current project specific footprint library table to path on file save
  as or empty project path.
* Fix a bug in Pcbnew in file save function that would silently overwrite
  an existing board file.
* Disable selecting the current library in the module editor when there are
  no libraries defined.
* Catch exceptions and report errors when writing footprint library tables.
* Fix Boost build CMakeFile to fix bug when bootstrapping a Boost build in
  MSys.
specctra_export.cpp: fix a bug in my export function to 3D viewer which generates bad shapes for holes generated by outlines
inside the main board outlines.
specctra_export.cpp: always approximate arcs in outlines by 36 segm for 360 degrees,
even for arc angle which differs from 90 degrees.
90 degrees is the default when creating an arc, but the arc value can be edited and have any value between 0 and 360 degrees.
Previously, 9 segments were used regardless the arc angle.