tex-babel{,-doc}: update to 3.73

3.73
This release just fixes a severe bug introduced in version 3.72 when
amsmath is loaded.

3.72
* Advances in amsmath (lua).
* Fixes:
  - Captions in Thai.
  - Some settings sometimes ignored with 'onchar' (lua).
  - Extra colon in Polish 'cc'

3.71
* IAST transliteration for Sanskrit (by Maximilian Mehner).
* Fixes:
  - Bad interraction between bidi option and mathtools
  - 'provide+=' didn窶冲 work with 'hebrew' as a secondary
    language.
  - Wrong equation direction in 'cases' and 'array'

3.70
* Finnish: transform 'prehyphen.nobreak'.
* Better fixes for amsmath, as well as for the default
  'equation' and 'eqnarray' (but still not perfect).
* Fix an error with bidi=basic and some fonts for graphics.

(markd)