SELinux support (at least on some ROMs)

* Added option to symlink hosts file to /data/hosts
* Added setting SELinux context on symlink target
Small improvement in SELinux support for symlink

Call chcon before chown/chmod. This way command block won't return
non-zero error code on Android versions without SELinux.
RootCommands: Properly close streams

Close streams after shell process termination. This fixes some
ANRs/crashes while doing root operations (at least on some
ROMs/Superuser solutions). These changes may require testing on other
ROMs/configurations. Changes introduced:
* Wait for shell process exit before closing stdin
* Reduce CPU usage (by 50 ms delays) while waiting for new commands
* After shell process exit close stdout/stderr
Fixed Hide reboot dialog setting

Fixed Hide reboot dialog setting being ignored after symlink creation
Updated help (all updates are english)
Merge pull request #536 from DavisNT/master

SELinux support (at least on some ROMs) + root fixes