Squashed 'ext/ucamlib/' changes from 6a15801..682f60b

682f60b Updated starts_with in ustring.
e450e85 Added USys to libs list.
363f4b4 Updated ucamlib
764c1ac Working on automating c file testing.
5844435 Added module USys and commadn shellcmd
7fa3577 Added two ustring functions.

git-subtree-dir: ext/ucamlib
git-subtree-split: 682f60bad1da81394adc2c4f909d64f54585daa5
Updated ucamlib and fixed a bug.