Add FIXME note about shallow clones

mkit/include/common.sh

     # meta-data is to *identify* the code, and provide safe path back
     # to tree; commit refs are already perfect for that.
     #
+    # FIXME:  The assumpton "if we are in git repo, we can read version
+    #         from tags" fails if we are in shallow clone made from
+    #         other than a tagged commit.
+    #
     local version=$VERSION
     local stage=$STAGE
     if git rev-parse HEAD >&/dev/null;