honor the --docdir configure option.  The projdocdir variable is replaced by docdir variable. projdocdir had the same functionality as --docdirconfigure option.  The default docdir value is: $(prefix)/share/doc/$(PACKAGE) (is the same as --enable-fhs option)
Merge pull request #1017 from basvandervlies/respect_docdir_option

honor the --docdir configure option.