Stop installing two unneeded files, including perf suite

Perf suite contains many files with dubious licensing and is
typically not useful in normal use. Since ed38447 it's no longer
needed to run tests.
Add docdir, mandir and man1dir environment variables for make install

Also change the default path for documentation to something more standard.
Copy doc/ and examples/ under $(build_docdir) instead of creating symlinks
as before, so that we don't need to remove unwanted files afterwards.
Finally, fix code relying on old paths.
Merge pull request #8428 from nalimilan/makeinstall

Make install cleaning and improvements