Updated `libsite.sh': new, fix, cleanup

New:

    New `core:imported()' function to check if a previous
    `core:softimport()' on a fiven module was successful or not.

    The deadman touch-file now contains the traceback to aid
    troubleshooting.

    `Makefile' updated with the ${SITE_SCM} path again, with a
    symbolic link that points to it from `~/.site/.scm'; mostly for
    unit-testing.
Updated `module/git': closes nima/site#9