Add method JGitUtils.createRepository(folder, name, shared) to create a new
repository as if it was created with the --shared command line switch of git.
Add proper implementation of methods in JnaUtils.

Implement the methods getFilemode and setFilemode
in JnaUtils. Not using the libc names as we don't
necessarily use JNA and because it is not necessarily
a one to one mapping.
Implement adjusting file permissions for shared repositories.

Implement adjusting file and directory permissions for shared
repositories in JGitUtils.
Add new property git.createRepositoriesShared.
Add JavaDoc.
Adjust unit tests for Windows.
Add commons-io to explicit dependencies.

Add the commons-io library explicitly to the depencencies.
It was already present as a transitive dependency but is now used in code.
Using the version 2.2 as that got so far already packaged in ext.
Remove unsupported option '-O' from 'ls' command.
Fix setting wrrong custom mode on file and in config.
Fix set-gid bit clearing under Linux when effective gid is different from file gid.