Add the path to the rethrown exception in case the zipfs can't be ope…

…ned (#71)

src/main/java/cpw/mods/niofs/union/UnionFileSystem.java

@@ -83,6 +83,10 @@ private static class UncheckedIOException extends java.io.UncheckedIOException {
         public UncheckedIOException(final IOException cause) {
             super(cause);
         }
+
+        public UncheckedIOException(final String message, final IOException cause) {
+            super(message, cause);
+        }
 
         @Override
         public synchronized Throwable fillInStackTrace() {
@@ -139,9 +143,9 @@ private static Optional<EmbeddedFileSystemMetadata> openFileSystem(final Path pa
             }
             return Optional.of(new EmbeddedFileSystemMetadata(path, zfs, fci));
         } catch (IOException e) {
-            throw new UncheckedIOException(e);
+            throw new UncheckedIOException("Failed to open file system from path " + path, e);
         } catch (Throwable t) {
-            throw new IllegalStateException(t);
+            throw new IllegalStateException("Failed to open file system from path " + path, t);
         }
     }