the 'Resource' module is a simple  interface for System.Plugins
new 'aotmp' directories; removed old exceptions for aoExec
new environment variable: AO_TEMP
 currently used for System.Plugins based JIT

simpler output for `ao jit`
now using the System.Plugins instead of System.Eval

note: currently, this probably leaks memory:

* GHC doesn't unload object code before 7.8.1 (Ubuntu ships 7.6.3)
* it isn't clear to me whether it requires explicit unload

Anyhow, it should be suitable actual use at this point, so long as
developers use it sparingly.
minor tweak to avoid hashing the ABC code twice.