Compiling 10459 java files when 1 is all that is needed.

[Phil Race]

I am getting very frustrated trying to do some simple work
on my Mac using JDK 8. I touch *one* .java source file and
I have to wait > 4 minutes for the build system which goes
off and compiles everything. I have an SSD and i7 chip
so I don't want to imagine what it would be like on a slower
system :

## Starting jdk
Compiling 10459 files for BUILD_JDK
....
....
....
## Finished jdk (build time 00:04:07)

Why is it doing this ?

-phil.