[PhingTask] Added output argument.

[siad007]

Log output to a file:

    <phing phingfile="phing.xml" target="dummy" output="test.log" />

Related to #1241

[codecov]

Codecov Report

Merging #1291 into master will increase coverage by 0.14%.
The diff coverage is 87.50%.

@@             Coverage Diff              @@
##             master    #1291      +/-   ##
============================================
+ Coverage     51.06%   51.21%   +0.14%     
- Complexity     9288     9294       +6     
============================================
  Files           479      479              
  Lines         22721    22737      +16     
============================================
+ Hits          11603    11645      +42     
+ Misses        11118    11092      -26     

Impacted Files	Coverage Δ	Complexity Δ
classes/phing/tasks/system/PhingTask.php	75.45% <87.50%> (+0.94%)	79.00 <1.00> (+6.00)
classes/phing/listener/DefaultLogger.php	78.20% <0.00%> (+35.89%)	36.00% <0.00%> (ø%)

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