Added HangDetectorPropertyTask to the PropertyTask tests.

I want to add some tests that currently fail to detect a circular
reference, but running these tests (obviously) causes PHPUnit to
hang which is very unpleasant.

HangDetectorPropertyTask extends PropertyTask and uses a custom
HangDetectorProperties (extends Properties) that counts the number
of accesses. More than 100 is interpreted as an undetected circular
reference. Don't use big property sets when testing...
Changed test3 to testCircularReferenceDetection and added data provider.
Add two new PropertyTask tests where circular definition detection fails.

Below, A->B means resolves to B in some way, like A=xx${B}yy

Currently a chain like A->B->A will be detected in the
resolveAllProperties() function since we check each new property in the
chain against the property were trying to resolve.

This fails if we start to resolve A but the circular chain doesn't
involve A:
A->B->C->B->C->B....

These two tests reflect that.
For consistence, it's circular "Definition", not "Reference".
Fix for the tests testCircularDefinition1 and testCircularDefinition2.

In resolveAllProperties() we remember which properties from $props have
been used to resolve the current property. If the same property appears
twice, we have a circular property definition.

This will detect chains like A resolves to B resolves to C resolves to B...
Forgot to add file...
remove tabs and trailing whitespace from docs
fix filelist typo and add link to fileset
fileset: add selectors as nested tags
add docs for pearpackagefileset
Created JsHintTask to allow JSHint check of JavaScript files
Merge pull request #237 from mhujer/jshint-task

Created JsHintTask to allow JSHint check of JavaScript files
Merge pull request #274 from cweiske/nodoctabs

docs for pearpackagefileset
Temporarily disable 5.6 builds (breakages)
replace ForeachTask::createFileSet() with addFileSet()
Use parent class add*() method if the task has no creator/adder
for the class itself.

This allows using PearPackageFileSet with all tasks that have a
addFileSet() method.
replace createFileSet() with addFileSet() wherever possible
adopt pearpackagefileset documentation example to new syntax
Unit test for bug #1090: PearPackageScanner and baseinstalldir

Followup of pull request #271.
Add support for <install as=""/> in pear package files.