[WISHLIST] add "/etc/default/tmpfs" logic like Debian's sysvinit

sysvinit 2.88dsf-23 introduced "/etc/default/tmpfs" in order to control whether to mount "/tmp" as a tmpfs filesystem as well as to control the size of tmpfs filesystems individually and overall.

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: upstart 1.10-0ubuntu7
ProcVersionSignature: Ubuntu 3.11.0-13.20-generic 3.11.6
Uname: Linux 3.11.0-13-generic x86_64
ApportVersion: 2.12.5-0ubuntu2.1
Architecture: amd64
Date: Tue Nov 12 04:51:13 2013
MarkForUpload: True
ProcKernelCmdline: BOOT_IMAGE=/boot/vmlinuz-3.11.0-13-generic.efi.signed root=UUID=9207cce1-beef-4f52-940d-2e742334d015 ro acpi_backlight=vendor ipv6.disable=1 consoleblank=0
SourcePackage: upstart
UpgradeStatus: No upgrade log present (probably fresh install)
UpstartBugCategory: System
UpstartRunningSessionVersion: init (upstart 1.10)
UpstartRunningSystemVersion: init (upstart 1.10)