Bugfix: undefined htmldir in config.mak.autogen

Html documents will be installed to root dir (/) no matter what prefix is set, if run these commands before `make` and `make install-html`: $ make configure $ ./configure --prefix=<PREFIX> After the installation, all the html documents will copy to rootdir (/), and: $ git --html-path <PREFIX> $ git help -w something fatal: '<PREFIX>': not a documentation directory. This is because the variable "htmldir" points to a undefined variable "$(docdir)" in file "config.mak.autogen", which is generated by running `./configure`. By default $(docdir) generated by configure is supposed be set this way: datarootdir='${prefix}/share' htmldir='${docdir}' docdir='${datarootdir}/doc/${PACKAGE_TARNAME}' but since fc1c5415d69d (Honor configure's htmldir switch, 2013-02-02), we only set and export htmldir without doing so for PACKAGE_TARNAME (which is set to 'git' by the configure script). Add the required two variables "PACKAGE_TARNAME" and "docdir" to file "config.mak.in" will work this issue around. Signed-off-by: Jiang Xin <worldhello.net@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>