Added compatibility for RRDtool 1.3.x, Added missing include

[bbczeuz]

• Fixed missing include warning (gcc 4.4.7-11 RHEL 6)
• Added compatibility for RRDtool 1.3.x line (RRDtool 1.3.x does not export rrd_info_r)

Reasons:

• RHEL 6 still uses RRDtool 1.3.8 in the default "supported" repositories. RHEL 6 will be supported until 2020 (End of "Production Phase 3", https://access.redhat.com/support/policy/updates/errata).

Check:

• This patch enables the RRDtool 1.3.x workaround PER DEFAULT. Please check if this breaks anything with the 1.4.x line, as I do not have access to any RRDtool 1.4.x

This patch is equivalent to: https://github.com/bbczeuz/facette/commit/3bf5c15ce7963ce3eea7943f939901bb709f3918

[bbczeuz]

Just for the logs: In order to support older RRDtool, changes in the application code may be needed, too, as RRDtool's variable names seem to have changed (See downstream patch: https://github.com/bbczeuz/facette/commit/3bf5c15ce7963ce3eea7943f939901bb709f3918)