Created by: Xerkus
Set values of BOOTSTRAP_LESS and BOOSTRAP_RESPONSIVE_LESS only if they not already set
When twitter boostrap makefile used in sub-make call, BOOTSTRAP_LESS and BOOSTRAP_RESPONSIVE_LESS can be set and exported in parent makefile.
Created by: Xerkus
Set values of BOOTSTRAP_LESS and BOOSTRAP_RESPONSIVE_LESS only if they not already set
When twitter boostrap makefile used in sub-make call, BOOTSTRAP_LESS and BOOSTRAP_RESPONSIVE_LESS can be set and exported in parent makefile.