Allow an ObjectChecker to reject special characters for Windows

Allow an ObjectChecker to reject special characters for Windows

Repositories that are frequently checked out on Windows platforms
may need to ensure trees do not contain strange names that cause
problems on those systems. Follow the MSDN guidelines and refuse
to accept a tree containing a special character, or names that end
with " " (space) or "." (dot).

Since Windows filesystems are usually case insensitive, also reject
mixed case versions of the reserved ".git" name.

Change-Id: Ic3042444b1e162c6d01b88c7e6ea39b2a73c4eca