tg-{contains,info}.sh: adopt fer_branch_contains
Switch away from calling `git branch --no-color --contains` directly
and instead us the new fer_branch_contains function.
By doing this `git for-each-ref --contains` will automatically be
used when running Git prior to v2.7.0 but automatically emulated
using the old parse-branch-contains-no-color-output technique.
In addition, since the new fer_branch_contains function always
provides full ref names (even in emulation mode) any possible
ambiguity between refs/heads and refs/remotes names evaporates.
Furthermore, use of fer_branch_contains insulates the code from any
capricous change to the `git branch --no-color --contains` output
format in the future.
Signed-off-by: Kyle J. McKay <mackyle@gmail.com>