Don't treat link-time warnings as errors when linking with libbusybox

See http://review.cyanogenmod.org/#/c/46642/ for why this is necessary.

Change-Id: Ib97484755569fcafc062d3c39b2841581987ca72
Fix roots.c to use fs_mgr

Change-Id: Ie68daba5e014dff0c4998da85576f35abe8ad270
Merge branch 'cm-10.2' into martincz