Disable static libraries by default

Disable static libraries by default

Every source file is currently built twice by libtool, once for
the shared library and once for the static library. Static libs
are not commonly packaged by distros and slow down compilation
time by more than 50% compared to a shared-only build time.

Time for 'make -j 4':

      shared only: 2 mins  9 secs
  shared + static: 3 mins 26 secs

Time for non-parallel make

      shared only: 3 mins 32 secs
  shared + static: 5 mins 41 secs

Those few people who really want them, can pass --enable-static
to configure

Disabling them by default requires use of LT_INIT, but for
compat with RHEL5 we can't rely on that. So we conditionally
use LT_INIT, but fallback to AM_PROG_LIBTOOL if not present.