Bumped version number to 0.5-SNAPSHOT.
Improve error handling on FileSystem#listFiles (#249).

In later version of Hadoop, FileSystem.listStatus() may throw
FileNotFoundException instead of returning null.
Introduce API Compatibility Layer between Hadoop 1.x and 2.x. (#250).

Hadoop 2.x will break SOURCE compatibility from 1.x.
This commit keeps away some incompatible APIs into
com.asakusafw.runtime.compatibility package.
Batchapp should not use unstable APIs directly (#251).

TaskInputOutputContext will break binary compatibility
in later version (class -> interface).
It should be kept away from compilation results.

[IMPORTANT] This commit will break binary compatibility of
compilation results (Runtime-Version=4.1).
Improve local symlink file detection in cleaner (#252).

It seems that Hadoop 2.0 LocalFileSystem still does not support symlink.
Improve debug logs in TestDriver (#253).

This log appears on cleaning hadoop working directory before running tests.
HADOOP_HOME should not use by default in component properties (#254).

HADOOP_HOME is deprecated in recent version of Hadoop.
Changed dependency of testing libraries to recent versions (#255).

Introduced JUnit 4.11 and Hamcrest 1.3.
Changed asakusafw version to 0.5.0 (#256).
Changed default dependency version of Hadoop library (#248).
Merge remote-tracking branch 'private/issue/248' into 0.5-develop
Merge remote-tracking branch 'private/issue/249' into 0.5-develop
Merge remote-tracking branch 'private/issue/250' into 0.5-develop

Conflicts:
	core-project/asakusa-runtime/src/main/java/com/asakusafw/runtime/directio/hadoop/HadoopDataSourceUtil.java
Merge remote-tracking branch 'private/issue/251' into 0.5-develop
Merge remote-tracking branch 'private/issue/252' into 0.5-develop
Merge remote-tracking branch 'private/issue/253' into 0.5-develop
Merge remote-tracking branch 'private/issue/254' into 0.5-develop
Merge remote-tracking branch 'private/issue/255' into 0.5-develop
Merge remote-tracking branch 'private/issue/256-M0' into 0.5-develop
Fixed #257.