Changes related to HTTP authentication handling. Also added a few small improvements to the original implementation in the develop branch.

Conflicts:
	library/Solarium/Core/Client/Adapter/PeclHttp.php
	library/Solarium/Core/Client/Request.php
	tests/Solarium/Tests/Core/Client/Adapter/HttpTest.php
	tests/Solarium/Tests/Core/Client/RequestTest.php
	tests/Solarium/Tests/QueryType/Select/Result/Spellcheck/SpellcheckTest.php