[freebsd91p7] Remove screen folder environment due to no permission.
[freebsd91p7][bash] moving machine dependent configs in .bash_postrc.
[freebsd91p7][env] Sync origin/cygwin for below commits.

1. [cygwin][vim] New bash command lviproj to view all files in current
                 session.
2. [cygwin][vim] Re-design session-auto feature. Using vi-proj to trigger.
3. [cygwin][git] Use git difftool to keep git diff behavior.