FS: Allow cloning an FS instance

This permits an application to create its own copy of FS.DETECTED
before manually setting the userHome or gitPrefix.

Bug: 337101
Change-Id: Ieea33c8d0ebdc801a4656b829d2a4b398559fd45
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java

 		// Do nothing by default.
 	}
 
+	/**
+	 * Initialize this FS using another's current settings.
+	 *
+	 * @param src
+	 *            the source FS to copy from.
+	 */
+	protected FS(FS src) {
+		userHome = src.userHome;
+		gitPrefix = src.gitPrefix;
+	}
+
+	/** @return a new instance of the same type of FS. */
+	public abstract FS newInstance();
+
 	/**
 	 * Does this operating system and JRE support the execute flag on files?
 	 *

org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX.java

 		return null;
 	}
 
+	FS_POSIX() {
+		super();
+	}
+
+	FS_POSIX(FS src) {
+		super(src);
+	}
+
 	@Override
 	public ProcessBuilder runInShell(String cmd, String[] args) {
 		List<String> argv = new ArrayList<String>(4 + args.length);

org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX_Java5.java

 import java.io.File;
 
 class FS_POSIX_Java5 extends FS_POSIX {
+	FS_POSIX_Java5() {
+		super();
+	}
+
+	FS_POSIX_Java5(FS src) {
+		super(src);
+	}
+
+	@Override
+	public FS newInstance() {
+		return new FS_POSIX_Java5(this);
+	}
+
 	public boolean supportsExecute() {
 		return false;
 	}

org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX_Java6.java

 		}
 	}
 
+	FS_POSIX_Java6() {
+		super();
+	}
+
+	FS_POSIX_Java6(FS src) {
+		super(src);
+	}
+
+	@Override
+	public FS newInstance() {
+		return new FS_POSIX_Java6(this);
+	}
+
 	public boolean supportsExecute() {
 		return true;
 	}

org.eclipse.jgit/src/org/eclipse/jgit/util/FS_Win32.java

 				&& StringUtils.toLowerCase(osDotName).indexOf("windows") != -1;
 	}
 
+	FS_Win32() {
+		super();
+	}
+
+	FS_Win32(FS src) {
+		super(src);
+	}
+
+	public FS newInstance() {
+		return new FS_Win32(this);
+	}
+
 	public boolean supportsExecute() {
 		return false;
 	}

org.eclipse.jgit/src/org/eclipse/jgit/util/FS_Win32_Cygwin.java

 		return cygpath != null;
 	}
 
+	FS_Win32_Cygwin() {
+		super();
+	}
+
+	FS_Win32_Cygwin(FS src) {
+		super(src);
+	}
+
+	public FS newInstance() {
+		return new FS_Win32_Cygwin(this);
+	}
+
 	public File resolve(final File dir, final String pn) {
 		String w = readPipe(dir, //
 				new String[] { cygpath, "--windows", "--absolute", pn }, //