[8u20] Request for approval: 8035891: javac, rename method asFree() in InferenceContext to asUndetVar() which reflects better it's purpose

[Vicente-Arturo Romero-Zaldivar]

Hi,

This is a backport of  refactoring subtask that was targeted for 9 but 
new changesets applied to 9 and to be bacported to 8u20 depend on this 
code. Please consider it to be pushed to 8udev.

Original bug: https://bugs.openjdk.java.net/browse/JDK-8035891
jdk9 changeset: 
http://hg.openjdk.java.net/jdk9/dev/langtools/rev/35789cbea856

Thanks,
Vicente