Enable mounting subdirectories

[proximous]

My nfs server shares "/nfs", but I like to mount "/nfs/Public". This changes the check_remoteshare function to check for the base folder being shared instead of the full path.

I chose a pure bash method to get the base folder (no reliance on awk/cut/etc) found here: http://stackoverflow.com/questions/24631866/how-to-get-root-directory-of-given-path-in-bash