RFR: 8171412: tools/javac/modules/AddLimitMods.java failed with "error: module not found"

[Jonathan Gibbons]

Relatively simple fix for module initialization.

javac was not correctly allowing for a qualified export to a 
non-existent module.
It handles the case where the reference was in a source file, but not in 
a compiled module.

The fix is to check for the existence of modules when expanding the 
command-line
option tokens ALL-SYSTEM and ALL-MODULE-PATH, so that non-existent 
modules are
ignored.

JBS: https://bugs.openjdk.java.net/browse/JDK-8171412
Webrev: http://cr.openjdk.java.net/~jjg/8171412/webrev.00/

-- Jon