Bug 961339 - Fix generated/ source dependencies. r=glandium

Generated sources are listed like 'generated/FILE.java'.  Generated
sources are produced by PP_TARGETS, which generates the file
'$(CURDIR)/generated/FILE.java'.  Because Make interprets $(CURDIR)/foo
and foo differently, this means we need to depend on $(CURDIR)/* for all
generated sources.  Since R.java is both listed as a generated source,
but produced by aapt, we need any dependencies to be on
$(CURDIR)/.../R.java.

The change to java-build.mk includes $(CURDIR) in the dependencies for
generated sources.  The changes to Makefile.in includes $(CURDIR) in the
produced R.java files for Make.
Bug 946083 - Part 1: Delete .class files when (re-)building a Java JAR. r=glandium

This cleans up stale .class files, so they don't get packaged into the
.jar files that Proguard consumes.
Bug 946083 - Part 2: Add dependencies for Proguard input jars. r=glandium

This restores no-op builds.