Clean fonts and docs makefiles, trying to fix 'make -j' race conditions

Clean fonts and docs makefiles, trying to fix 'make -j' race conditions

On my machine (GNU/Linux Fedora 17 x86_64 on an Intel Core 2 Duo),
"make -j3 all" repeatedly calls fontforge before needed .pfb files are
generated and makeinfo/extract_texi_filenames/texi2omf before .texi
file has been generated/copied.  Fix this by using order prerequisites
and adding targets to WWW-1 (first stage of doc build); order (rather
than ordinary) prerequisites avoid having always outdated targets,
which would trigger compilation at install.

Remove a rule for Info manual that is no longer needed and which might
short-circuit .dep file generation.

mf/GNUmakefile: also factorize prerequisites in fonts using a macro.