Better git commmand and less output

Git has better methods to read the changed files than `git status`.

The pre-commit hook should check only staged files and not all changed files in the working tree.

This change removes some output like which file is being checked as it is not needed.

Less output for successful checks comply with the rule of silence from the Unix philosophy: 
http://www.catb.org/~esr/writings/taoup/html/ch01s06.html#id2878450
Merge pull request #1 from hkdobrev/patch-1

Better git commmand and less output