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Warning: Extremely Boring, Project-Specific Post

Onto the next puzzle: I'm trying to compile without importing any JCL code, in order to find out what JRE code needs to be emulated that is not covered by GWT. I'm getting this very peculiar output:

Buildfile: /home/jacob/workspace/gsoc-phase-1/org.eclipse.swt.e4.examples/dojo/build.xml

init:

build-dojo:
        [java] WARNING: 'com.google.gwt.dev.GWTCompiler' is deprecated and will be removed in a future release.
        [java] Use 'com.google.gwt.dev.Compiler' instead.
        [java] (To disable this warning, pass -Dgwt.nowarn.legacy.tools as a JVM arg.)
        [java] Compiling module controlexample
        [java]    Refreshing module from source
        [java]       Validating newly compiled units
        [java]          Removing units with errors
        [java]             [ERROR] Errors in 'file:/home/jacob/workspace/gsoc-phase-1/org.eclipse.swt/Eclipse%20SWT/common/org/eclipse/swt/internal/image/PNGFileFormat.java'
        [java]                [ERROR] Line 294: The method getProperty(String) is undefined for the type System
...

Why on earth is the GWT compiler trying to go inside of org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/internal?