bump version to 315.2.2

バージョンを315.2.2にしてtagを打っていただけると助かります（315.2.1にすべきですが，諸般*の事情で３１５．２．１を欠番にしてもらえると嬉しいです．．．ダメなら315.2.1で構いません）

* start-jsk/hrpsys/package.xmlで先走って315.2.1を打ってしまった．
```
74d07f9 (lib/util/CMakeLists.txt) : forget to install Hrpsys.h (24c6139826)
0303d15 (rtc/PlaneRemover) adds a configuration variable pointNumThd to specify the minimum number of points to define a plane
f34f28b (rtc/PlaneRemover) adds return value of setConfiguration() and setProperty()
85afa1c (rtc/ThermoLimiter/) Removed TwoDofController, which is not used in ThermoLimiter now
63f3ae7 (python/hrpsys_config.py) add getRTCList for unstable RTCs
9eb3a12 (rtc/SORFilter) fixes typos(again)
233a31a (rtc/PlaneRemover) adds a new component, PlaneRemover
26f2f09 (rtc/SORFilter) fixes typos
c5a8ee5 (rtc/TorqueFilter) Modified debug message position for tf params
9c13ee2 (rtc/TorqueFilter) Added timestamp to tf.rtc:tauOut and modified method to deal with input error
de0b63e (rtc/TorqueFilter) Modified and supressed error messages for TorqueFilter
6ebcb7b (rtc/TorqueController) Supress error message by debugLevel and output qRefIn to qRefOut when torque controller does not work due to some fault of input.
eafe5f5 (rtc/PCDLoader) adds a new component, PCDLoader
```