The flag handling (both compiler options and include paths) are a mess at
the moment.  There is no point in forcing "-O2 -g" when these are already
the defaults, and if someone changes the defaults, chances are good they
don't want you clobbering their choices.

The -Wall flag should be handled in configure and thrown into CFLAGS once
rather than every Makefile.am.  Plus, this way we can control which
compilers the flag actually gets used with.

Finally, the INCLUDES variable is for -I paths, not AM_CFLAGS.  Nor should
it contain -I. as this is already in the default includes setup.
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Thanks to Guillaume Rousse, we now use libtool to build shared libraries.

Thank you very much, Rohit!