kernel/linux: allow headers from full custom source tree
Accept a local tarball name as the source of the Linux kernel headers,
rather than forcing the user to use either an upstream tarball, or a
local pre-installed headers tree.
1 This is NOT the official version of dialog. This version has been
2 significantly modified from the original. It is for use by the Linux
3 kernel configuration script. Please do not bother Savio Lam with