Issue #1096340 by plach, fietserwin, sun: Fixed Stale language types/negotation info after enabling/disabling modules.

#587706 follow-up by plach: trim GET['q'] centrally in request_path() so subsequent places don't have to do it.

#282191 follow-up by plach: Remove ambitious parts of translatable fields UI from core that are no longer relevant, given what made it into Drupal 7.

#587706 by dalin: Fixed language_initialize() needs to clean up ['q'] just like drupal_path_initialize() does.

#678546 by rfay and jhodgdon: Improve wording of help text in admin/config/regional/language/configure.

#320331 by Dave Reid, dww, John Morahan, cwgordon7, moshe weitzman, c960657, and smoothify: Turn custom_url_rewrite_inbound() and custom_url_rewrite_outbound() into hooks.

#565480 by plach and peximo: TF #2: Multilingual field handling. Integration between field API and locale module + translatable node bodies.

- Patch #262920 by ainigma32: language selection for domain should look at HTTP_HOST not SERVER_NAME.

- Patch #245115 by kkaefer, John Morahan, JohnAlbin et al: after a long discussion we've decided to make the concatenation operator consistent with the other operators.

#202925 report by beholder, patch by myself: (notice fix) only consider languages with a host set when comparing with the current host in domain language negotiation

 - whitespaces at end of lines
 - indentation
 - control structure usage
 - whitespace in empty lines
 - phpdoc comment formatting

#196410 report by daniel.soneira, patch by myself, tested by Freso: several fixes to url() generation and path aliasing, fixing path aliases for node paths and front page links in themes

#194743 by myself, reported and tested by Murz: the base URL was not properly modified for outgoing links to different language domains and path aliases were not handled in the target language

#194743 report by Murz, patch by myself: in domain language negotiation mode, we should tell url() that we built an external URL, not that we need an absolute URL built by url()

- Patch #144634 by chx: fixed critical bug that prevented language negotiation to work after/when drupal_goto() is called.

#173274 by Desbeers: treat <front> as the empty path, when adding path prefixes, so we get the proper result

#158452 by kenji_kun, patch by myself: GET['q'] might not be defined at the language bootstrap phase

Leftover variable name spotted by Amr Mostafa, reported by email (because 'the fix is too small and trivial to submit an issue')