Allow Interval per File block for tail plugin

The allows each <File> block in the tail plugin config to specify
its own Interval value. If ommitted, will use the default.
Add ReportByCpu and ValuesPercentage for cpu plugin

ReportByCpu defaults to true, ValuesPercentage to false

This enables the following use cases:

- ReportByCpu false: emits normalized percentage values
- ValuesPercentage true: emits percentage values
- default: send per core ticks, as previously
handle comments from @octo
fix typos
keep plugin instance for first cpu
add a value_to_rate function.
as advised by @octo move to a rate computing function
typo fixes.
Merge branch 'master' into feature-normalized-cpu
better indentation.
Fix tcp state names to be like others.
memory plugin: fix submit multivalue (fill vl.type)
HTTP Digest support for curl plugins
indents
AIX doesn't have MSG_DONTWAIT, define as MSG_NONBLOCK
write_riemann: send notification message to riemann via description field
Merge pull request #516 from pyr/feature-normalized-cpu

Add ReportByCpu and ValuesPercentage for cpu plugin
add documentation for #516
typo in plugin descr header
Merge pull request #575 from amiron/riemann_notification_message

write_riemann: send notification message