Split build options files into a static set of defaults

Split build options files into a static set of defaults
for committing to bk and a dynamically updated set which
are not under revision control.

build/SConstruct:
    Split build options into static defaults and dynamic "current" settings.

--HG--
rename : build/build_options/ALPHA_FS => build/build_options/default/ALPHA_FS
rename : build/build_options/ALPHA_FS_TL => build/build_options/default/ALPHA_FS_TL
rename : build/build_options/ALPHA_SE => build/build_options/default/ALPHA_SE
extra : convert_revision : 8219211a3f2ce955fd6e2c34c169cac3fc704854