Fix broken download_boost.cmake. Fix minor other issues:
dialog fp lib table display not updated (Windows specific) when an option is changed from the lib table option editor
overloaded function in dialog_fp_lib_table.cpp not compiled with gcc 4.4.7 (try to fix Bug #1262002).
specctra_export.cpp: set min dist to find segment ends when building the board outline to 2 microns (should break anything, but should be enough to fix rounding issues when creating/importing board outlines with arcs)