Rename default options path from "build_options/default" to "default_options",

Rename default options path from "build_options/default" to "default_options",
and current options path from "build_options/current" to "options".
This way we can symlink default_options to a different build dir
w/o clobbering the current options.

--HG--
rename : build/build_options/default/ALPHA_FS => build/default_options/ALPHA_FS
rename : build/build_options/default/ALPHA_FS_TL => build/default_options/ALPHA_FS_TL
rename : build/build_options/default/ALPHA_SE => build/default_options/ALPHA_SE
rename : build/build_options/default/MIPS_SE => build/default_options/MIPS_SE
rename : build/build_options/default/SPARC_SE => build/default_options/SPARC_SE
extra : convert_revision : 8c0d3139cdd7e9ed40a9f2deeb47f65f24e52799