It then looks like those two variables are not used as detailed in the
documentation (info -f grub -n 'Simple configuration'):
`GRUB_CMDLINE_LINUX'
Command-line arguments to add to menu entries for the Linux kernel.
`GRUB_CMDLINE_LINUX_DEFAULT'
Unless `GRUB_DISABLE_RECOVERY' is set to `true', two menu entries
will be generated for each Linux kernel: one default entry and one
entry for recovery mode. This option lists command-line arguments
to add only to the default menu entry, after those listed in
`GRUB_CMDLINE_LINUX'.
Anyway. I am glad you can now normally boot from GRUB. As for updating the
kernel, there are two simple solutions. You can either opt for the 3.5
version, which is directly available in Trisquel 6.0's repository (install
the package named "linux-generic-lts-belenos") or constantly stick to the
latest version by adding jxself's repository for Linux-libre (follow this
documentation). Of course, the latter option is somewhat more dangerous for
the stability of your system. Always keep an older working kernel in
parallel.
