Log Message:
tex-babel{,-doc}: update to 3.18

3.18
- More bidi in luatex: captions (required only in multilingual
  docs) and tabular (required for R tables). Also an experimental
  support for captions in xetex and pdftex (tabular is not yet
  supported).
- New ini files: ar-DZ, ar-MA, ar-SY
- Fix - \begin{hyphenrules} didn't work with polyglossia.
- Fix - switch.def was loaded twice.

3.17
- A tool for bidi footnotes.
- Fix -- \ragged... didn't work for bidi.

3.16
 - New package option layout for bidi documents.

 - Quotes in TU encoding

 - Fix - \<language>date did not work correctly

 - Fix - with some languages (eg, british), using
   \babelfont raised an error.

3.15
New command \babelfont (in Unicode engines) to define
language/script dependent fonts. Related to it, new
keys (script, language) in \babelprovide.

A common mistake is to leave some space(s) in
\captions<lang>, which go to the document. Now babel
removes them.

A couple of fixes:

- Error with hyphenrules in \babelprovide in some cases.
- \hyphenrules doesn't set \languagename any more (which
  was against the documented behavior).