Add ability to "save" NLI sessions

[GoogleCodeExporter]

Two thoughts: 

Replay:
one is to "save" the incrementally emitted assemblies "as is"... this means 
"loading" would be more like a replay (go through each type's static 
constructor, each field will be set anew -- has implications for side-effects 
code).

Snapshot:
the other is to "save" a snapshot of all of the fields in all the emitted 
assemblies. we'd need to think of another strategy than here; perhaps just go 
through all the fields of the emitted assemblies and gather into a dictionary 
and then serialize and save to disc. 

Original issue reported on code.google.com by [email protected] on 21 Dec 2011 at 8:33