Fix support for making scroll queries

Need to use the _search/scroll api endpoint.
Add tests for scroll search
Merge pull request #404 from jbafford/feature/scroll

Fix support for making scroll queries
Implement terms lookup for terms filter.
Implement terms lookup for terms filter.
Merge branch 'terms-lookup' of github.com:jlinn/Elastica into terms-lookup

Conflicts:
	test/lib/Elastica/Test/Filter/TermsTest.php
Change TermsTest index name to avoid conflict.

TermsTest created and deleted the 'elastica_test' index, which was presumed to exist by a subsequent test.  Since the index had been deleted, the later test failed.  Renaming the index used in TermsTest avoids this failure.
Merge pull request #406 from jlinn/terms-lookup

Terms lookup