Makefile: removed install-loaddefs target.

There is no rule for this target and it causes an error when invoking
"make install". loaddefs are installed by the "install-lisp" target so
there is no need for it anyway.
Makefile: use install-info to install info files by default.

install-info is available in most linux distributions while
ginstall-info is not.
Merge pull request #730 from bastianbeischer/makefile_fixes

Fixes to make install rules