gen_all_grammar: portability fixes

Instead of assuming that ROS_PACKAGE_PATH contains only one directory,
iterate through it correctly. Similarly, find the sub-directories
containing language models in a more portable fashion.
gen_grammar: raring fixes

In the latest Ubuntu, the mkdfa program no longer has a .pl extension.
Merge branch 'raring-fixes-2'
Merge branch 'gen-grammar-fixes'