Revert "JCLOUDS-652: Require JDK 7"

This reverts commit 5e8bd02c93c7ebacb573342e77ef7ca4b02c4ffb.
Revert "Remove Java 6 litter"

This reverts commit a10bf3e9c5495b4c8c69e0059b5901266df471dd.
Revert "JCLOUDS-264: Allow payloads greater than 2 GB"

This reverts commit 7e4cacf9ea12d697d6c48b83a28c12d47ab8cfae.
JCLOUDS-264 Conditionally allow default http driver to support sending >2GB payloads without chunked encoding.
Revert "Prefer ByteSource payload"

This reverts commit 0e3d1475ab50e1232d5eac16eee1d3a207e36f42.
JCLOUDS-652 Pin filesystem api to Java 7+.