dconf update: change error handling

Instead of just ignoring errors when trying to parse keyfiles in a .d
directory, fail the compile outright.  'dconf update' will print the
error and attempt to move on to the next .d directory in line.

https://bugzilla.gnome.org/show_bug.cgi?id=672303
dconf(1): some whitespace changes

Add some more padding to 'dconf help' output to accomodate coming
additions.

https://bugzilla.gnome.org/show_bug.cgi?id=672303
dconf(1): add 'dconf compile' command

This allows manually compiling dconf databases outside of /etc.  This is meant
to be used from the build system of projects that want to install dconf
databases (like gdm) to easily build the database in-tree.

https://bugzilla.gnome.org/show_bug.cgi?id=672303