Classes fail to load when not packaged with Parquet.

Parquet cannot dynamically load classes from another package. This has already been noticed and addressed here: https://github.com/Parquet/parquet-mr/pull/289

However, the fix didn't address all occurrences of Class.forName. parquet-cascading jobs fail trying to load cascading.scheme.Scheme, even though it is present on the classpath.

This bug shows up in cloudera distributions of parquet since they provide parquet jars on the hadoop classpath.

**Reporter**: [Alex Robbins](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=alexrobbins)

_{**Note**: *This issue was originally created as [PARQUET-261](https://issues.apache.org/jira/browse/PARQUET-261). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

首先查看 pull request 289，并定位与加载 cascading.scheme.Scheme 相关的剩余 Class.forName 出现位置。将 Parquet JAR 放在 Hadoop 类路径上，重现 parquet-cascading 失败，然后验证类路径上存在另一个包中的类时，这些类能够成功加载。

由索引模型根据 Issue 内容生成。