Fix javadoc error "class file for sun.util.resources.OpenListResourceBundle not found"

It seems to be a javac/javadoc bug.
See https://code.google.com/p/doclava/issues/detail?id=38

sun.util.resources.OpenListResourceBundle is a class defined in the host rt.jar,
but sometimes on some platform javadoc/javac can't find it.
-XDignore.symbol.file tells javadoc/javac to skip the stubs file ct.sym
and link against rt.jar directly.

Change-Id: I3930f7399fc14b2d6b43c29f737fa90f37515aff

core/droiddoc.mk

@@ -165,6 +165,7 @@ $(full_target): $(full_src_files) $(droiddoc_templates) $(droiddoc) $(html_dir_f
                 -encoding UTF-8 \
                 \@$(PRIVATE_SRC_LIST_FILE) \
                 -J-Xmx1280m \
+                -XDignore.symbol.file \
                 $(PRIVATE_PROFILING_OPTIONS) \
                 -quiet \
                 -doclet com.google.doclava.Doclava \
@@ -200,6 +201,7 @@ $(full_target): $(full_src_files) $(full_java_lib_deps)
                 $(PRIVATE_DROIDDOC_OPTIONS) \
                 \@$(PRIVATE_SRC_LIST_FILE) \
                 -J-Xmx1024m \
+                -XDignore.symbol.file \
                 $(PRIVATE_PROFILING_OPTIONS) \
                 $(addprefix -classpath ,$(PRIVATE_CLASSPATH)) \
                 -sourcepath $(PRIVATE_SOURCE_PATH)$(addprefix :,$(PRIVATE_CLASSPATH)) \