Add support for Cyrillic in Texinfo/TeX (issue 6492045)

[john . mandereau]

Reviewers: lilypond-devel_gnu.org,

Message:
This is a new version of Werner's patch (Rietveld issue 6459081), with
no changes to cyrillic.itexi, a configure check added, and the inclusion
of cyrillic.itexi moved to common-macros.itexi so that translated
manuals include it too.

Description:
Add support for Cyrillic in Texinfo/TeX

This is a follow-up of Rietveld Issue 6459081.

Please review this at http://codereview.appspot.com/6492045/

Affected files:
  M Documentation/common-macros.itexi
  A Documentation/cyrillic.itexi
  M configure.in