unpackfs: code dedup
unpackfs: check for supported filesystems

Use /proc/filesystems to check if the system
supportes the given source filesystem.
locale: make sure /etc/localtime doesn't exist

If /etc/localtime exists in source image, creating a new symlink will fail
and prevent the installer from doing it's job.
Merge pull request #102 from bbqlinux/master

Supported filesystems check in unpackfs, check for /etc/localtime.
Try to find settings.conf from SYSCONFDIR

Honor SYSCONFDIR as specified by CMake arguments instead of
using a hard-coded path.

Since GNUInstallDirs set CMAKE_INSTALL_FULL_SYSCONFDIR to
CMAKE_INSTALL_PREFIX/etc we need to change the default ourselves.
Merge pull request #106 from plfiorini/settingsconf

Try to find settings.conf from SYSCONFDIR