Issue #2187477 by lokapujya, vaibhavjain, visabhishek: Remove Unused use statements from system module.

Issue #2168113 by penyaskito, jessebeach, catch: Add leading underscore and other discouragement to drupal_add_css() and drupal_add_js().

Issue #1798738 by alexpott, mtift, tayzlor, ianmthomasuk, Albert Volkman, heyrocker, cam8001: Move css_js_query_string() to state system.

Issue #352951 by Wim Leers, mfer, mcjim, larowlan, RobLoach, sdboyer, Owen Barton, JohnAlbin: Make JS & CSS Preprocessing Pluggable.

Issue #2015789 by fubhy, echoz, rteijeiro, LewisNyman, penyaskito: Remove language_css_alter() (RTL stylesheets) in favor of HTML 'dir' attribute.

Issue #1924436 by JohnAlbin, rteijeiro: Remove separate CSS_AGGREGATE_SYSTEM aggregate file and fix drupal_add_library() to aggregate CSS properly.

Issue #1987066 by Kevin Morse, JohnAlbin, rteijeiro, echoz, ry5n: Rename files to match CSS file naming convention.

Issue #1620010 by dawehner, ParisLiakos, plach, jibran: Move LANGUAGE constants to the Language class.

Issue #1924368 by JohnAlbin, ykhadilkar, carwin: Change notice: Rename old CSS constants to CSS_AGGREGATE_* and add new CSS weight constants.

Issue #1818556 by das-peter, plach, fago, Berdir, vijaycs85: Change notice: Convert nodes to the new Entity Field API.

Issue #575298 by sun, tim.plunkett, Rob Loach, KrisBulman, Jacine, danillonunes: Provide non-PHP way to reliably override CSS.

Issue #1431658 by Albert Volkman, kid_icarus, ChinggizKhan, xjm, rgristroph, connork: Clean up API docs for many system tests

Issue #1431658 by Albert Volkman, xjm, kid_icarus, ChinggizKhan, rgristroph, connork: Massive API docs cleanup for system tests

Issue #1711070 by kid_icarus, tim.plunkett, xjm, droplet, zendoodles and cam8001: Convert tests to use ::$modules property instead of parent::setUp($modules).

Using the language_manager wrapper function to return a language whether or not we're in the requet scope

Issue #1071818 by JeremyFrench, nod_, reglogge, anthbel, xjm, sun, NROTC_Webmaster, lliss, Cottser: Fixed Lazy-loading CSS fails in IE.

- Patch #1510686 by cosmicdreams, vasi1186, webflo, disasm: replace remaining references to global () with drupal_container().