WARNING: this patch changes interface-file formats slightly
	 	 you will need to recompile your libraries

Duncan Coutts wanted to export a function that has a NOINLNE pragma
in a local let-defintion.  This works fine within a module, but was 
not surviving across the interface-file serialisation.

http://www.haskell.org/pipermail/glasgow-haskell-users/2007-March/012171.html

Regardless of whether or not he's doing something sensible, it seems
reasonable to try to retain local-binder IdInfo across interface files.
This initial patch just retains inline-pragma info, on the grounds that
other IdInfo can be re-inferred at the inline site.

Interface files get a tiny bit bigger, but it seesm slight.