Issues with documentation not compiling when changing lilypond-texi2html.init

[Carl Peterson]

When trying to work the Documentation/lilypond-texi2html.init file, I have
observed that changing this file does not trigger the documentation to
rebuild when running make. However,
changing Documentation/css/lilypond-manuals.css triggers the entire
documentation to rebuild. This seems backwards, since
lilypond-texi2html.init touches pretty much every part of the
documentation, and the css file isn't actually involved in compiling
anything.

The command being run to make the documentation for the website is:

make WEB_TARGETS="offline online" doc

per
http://lilypond.org/doc/v2.17/Documentation/contributor/debugging-website-and-docs-locally

Carl Peterson