smart: mention support lib in README
add credits for new plugins
RPM specfile: add support for smart & openldap plugins
libstatgrab: only use one configure test for 0.90 API change

Previously, each API change was tested in configure.ac. Some of the
tests are relying on signature checks and would need to have -Werror
flag enabled to make them work. This is quite fragile.

Instead, we assume that if `sg_init()` requires an argument, we must use
the 0.90 API.

Fixes: #795
Fix wrong #ifdef introduced in df46cd01
Detect sys/vmmeter.h and include it if available.

Needed on OpenBSD for struct vmtotal definition.
Merge pull request #808 from landryb/openbsd_build_fixes_2

Openbsd build fixes 2
Merge pull request #806 from vincentbernat/fix/libstatgrab2

libstatgrab: only use one configure test for 0.90 API change