Changes necessary for JDime wrapper script

To retrieve the information about the number of conflicts, a merge now returns the number of conflicted files instead of a Status object.

src/de/uni_passau/fim/gitwrapper/Reference.java

@@ -2,6 +2,7 @@ package de.uni_passau.fim.gitwrapper;
 
 import de.uni_passau.fim.processexecutor.ProcessExecutor;
 
+import java.nio.file.Path;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Objects;
@@ -126,6 +127,18 @@ public abstract class Reference {
         return revList.map(toParentsList);
     }
 
+    /**
+     * Checks whether this {@link Reference} contains the specified file.
+     *
+     * @param file
+     *          the (repository relative) path to the file to look for in this {@link Reference}
+     * @return {@code true} iff this {@link Reference} contains the file
+     */
+    public Optional<Boolean> hasFile(Path file) {
+        Optional<ProcessExecutor.ExecRes> result = git.exec(repo.getDir(), "cat-file", "-e", id + ":" + file);
+        return result.map(ProcessExecutor.ExecRes::succeeded);
+    }
+
     @Override
     public final boolean equals(Object o) {
         if (this == o) {