Added PhingVersion condition / task

Examples
```
    <phingversion property="phingversion"/>
```
Stores the current Phing version in the property phingversion.
```
    <phingversion property="phingversion" atleast="2.9"/>
```
Stores the Phing version in the property phingversion if the current Phing version is 2.9.0 or higher. Otherwise the property remains unset.
```
    <phingversion property="phing-is-exact-9" exactly="2.9.0"/>
```
Sets the property ant-is-exact-7 if Phing 2.9.0 is running. Neither 2.8.0 nor 2.8.2 would match.
```
    <condition property="Phing29isOnline">
      <and>
        <phingversion exactly="2.9.2"/>
        <http url="http://www.phing.info"/>
      </and>
    </condition>
```
Sets Phing29isOnline if Phing 2.9.2 is running and can get a non-error-response from the Phing homepage.