Changing annotation processing to use single Context for all rounds of annotation processing

[Jan Lahoda]

Hi Werner and others,

Currently, most of javac's services and data get cleared between 
annotation processing rounds. Lately, I've been working on a patch that 
would allow to keep as much as possible across rounds. The advantages 
include faster compilation (as ClassSymbols from classpath don't need to 
be read again and again for each annotation processing round) and 
cleaner javac internals.

My current patch is available here:
http://cr.openjdk.java.net/~jlahoda/2206926/webrev.01/

The patch should be applicable to current jdk9/dev/langtools and current 
type-annotations/langtools.

Any comments on the patch, or practical experiences running the Checker 
Framework (or any other annotation processor/framework) on a javac with 
this patch are very welcome and would be greatly appreciated.

Thanks,
     Jan