get ready for 1.7.0

add section on changes from 1.5 to 1.6

Disable nagel algorithm

Disable TCP's nagal algorithm which was causing massive slowdown
in processing rrdcached requests.

Also check for other setsockopt call errors.

get ready for 1.5.5

get ready for 1.5.4

ready for 1.5.3

prep for 1.5.2

Merge branch '1.5' of github.com:oetiker/rrdtool-1.x into 1.5

updated

test should not be dependent on the current time